Are static class variables possible in Python

Question

Is it possible to have static class variables or methods in Python  What syntax is required to do this

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So this is probably a hack  but I ve been using eval str  to obtain an static object  kind of a contradiction  in python 3   There is an Records py file that has nothing but class objects defined with static methods and constructors that save some arguments   Then from another  py file I import Records but i need to dynamically select each object and then instantiate it on demand according to the type of data being read in   So where object name    RecordOne  or the class name  I call cur type   eval object name  and then to instantiate it you do cur inst   cur type args  However before you instantiate you can call static methods from cur type getName   for example  kind of like abstract base class implementation or whatever the goal is   However in the backend  it s probably instantiated in python and is not truly static  because eval is returning an object    which must have been instantiated    that gives static like behavior

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Static methods in python are called classmethods  Take a look at the following code  class MyClass       def myInstanceMethod self           print  output from an instance method        classmethod     def myStaticMethod cls           print  output from a static method    gt  gt  gt  MyClass myInstanceMethod   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unbound method myInstanceMethod   must be called         gt  gt  gt  MyClass myStaticMethod   output from a static method   Notice that when we call the method myInstanceMethod  we get an error  This is because it requires that method be called on an instance of this class  The method myStaticMethod is set as a classmethod using the decorator  classmethod   Just for kicks and giggles  we could call myInstanceMethod on the class by passing in an instance of the class  like so    gt  gt  gt  MyClass myInstanceMethod MyClass    output from an instance method

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Static methods in python are called classmethods  Take a look at the following code  class MyClass       def myInstanceMethod self           print  output from an instance method        classmethod     def myStaticMethod cls           print  output from a static method    gt  gt  gt  MyClass myInstanceMethod   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unbound method myInstanceMethod   must be called         gt  gt  gt  MyClass myStaticMethod   output from a static method   Notice that when we call the method myInstanceMethod  we get an error  This is because it requires that method be called on an instance of this class  The method myStaticMethod is set as a classmethod using the decorator  classmethod   Just for kicks and giggles  we could call myInstanceMethod on the class by passing in an instance of the class  like so    gt  gt  gt  MyClass myInstanceMethod MyClass    output from an instance method

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To avoid any potential confusion  I would like to contrast static variables and immutable objects   Some primitive object types like integers  floats  strings  and touples are immutable in Python  This means that the object that is referred to by a given name cannot change if it is of one of the aforementioned object types  The name can be reassigned to a different object  but the object itself may not be changed   Making a variable static takes this a step further by disallowing the variable name to point to any object but that to which it currently points   Note  this is a general software concept and not specific to Python  please see others  posts for information about implementing statics in Python

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Personally I would use a classmethod whenever I needed a static method  Mainly because I get the class as an argument   class myObj object      def myMethod cls              myMethod   classmethod myMethod     or use a decorator  class myObj object       classmethod    def myMethod cls    For static properties   Its time you look up some python definition   variable can always change  There are two types of them mutable and immutable   Also  there are class attributes and instance attributes   Nothing really like static attributes in the sense of java  amp  c    Why use static method in pythonic sense  if it has no relation whatever to the class  If I were you  I d either use classmethod or define the method independent from the class

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If you are attempting to share a static variable for  by example  increasing it across other instances  something like this script works fine     - - coding  utf-8 - - class Worker      id   1      def   init   self           self name              self document              self id   Worker id         Worker id    1      def   str   self           return u    -        format self id  self name  self document  encode  utf8     class Workers      def   init   self           self list           def add self  name  doc           worker   Worker           worker name   name         worker document   doc         self list append worker    if   name         main         workers   Workers       for item in    Fiona    0009898      Maria    66328191      Sandra    2342184      Elvira    425872             workers add item 0   item 1       for worker in workers list          print worker      print  next id   i    Worker id

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Variables declared inside the class definition  but not inside a method are class or static variables    gt  gt  gt  class MyClass          i   3      gt  gt  gt  MyClass i 3    As  millerdev points out  this creates a class-level i variable  but this is distinct from any instance-level i variable  so you could have   gt  gt  gt  m   MyClass    gt  gt  gt  m i   4  gt  gt  gt  MyClass i  m i  gt  gt  gt   3  4    This is different from C   and Java  but not so different from C   where a static member can t be accessed using a reference to an instance   See what the Python tutorial has to say on the subject of classes and class objects    Steve Johnson has already answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class C       staticmethod     def f arg1  arg2               beidy recommends classmethods over staticmethod  as the method then receives the class type as the first argument  but I m still a little fuzzy on the advantages of this approach over staticmethod  If you are too  then it probably doesn t matter

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Not like the  staticmethod but class variables are static method of class and are shared with all the instances  Now you can access it like instance   MyClass   print instance i   or print MyClass i   you have to assign the value to these variables I was trying class MyClass    i  str  and assigning the value in one method call  in that case it will not work and will throw an error i is not attribute of MyClass

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One special thing to note about static properties  amp  instance properties  shown in the example below   class my cls    my prop   0   static property print my cls my prop   -- gt  0   assign value to static property my cls my prop   1  print my cls my prop   -- gt  1   access static property thru  instance my inst   my cls   print my inst my prop  -- gt  1   instance property is different from static property   after being assigned a value my inst my prop   2 print my cls my prop   -- gt  1 print my inst my prop  -- gt  2   This means before assigning the value to instance property  if we try to access the property thru  instance  the static value is used  Each property declared in python class always has a static slot in memory

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Put it this way the static variable is created when a user-defined a class come into existence and the define a static variable it should follow the keyword self  class Student       the correct way of static declaration     i   10      incorrect     self i   10

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Put it this way the static variable is created when a user-defined a class come into existence and the define a static variable it should follow the keyword self  class Student       the correct way of static declaration     i   10      incorrect     self i   10

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dataclass definitions provide class-level names that are used to define the instance variables and the initialization method    init      If you want class-level variable in  dataclass you should use typing ClassVar type hint  The ClassVar type s parameters define the class-level variable s type  from typing import ClassVar from dataclasses import dataclass   dataclass class Test      i  ClassVar int    10     x  int     y  int          def   repr   self           return f quot Test  self x     self y     Test i    quot   Usage examples   gt  test1   Test 5  6   gt  test2   Test 10  11    gt  test1 Test self x 5  self y 6  Test i 10   gt  test2 Test self x 10  self y 11  Test i 10

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Absolutely Yes    Python by itself don t have any static data member explicitly  but We can have by doing so   class A      counter  0     def callme  self           A counter   1     def getcount  self           return self counter    gt  gt  gt  x A    gt  gt  gt  y A    gt  gt  gt  print x getcount     gt  gt  gt  print y getcount     gt  gt  gt  x callme     gt  gt  gt  print x getcount     gt  gt  gt  print y getcount      output  0 0 1 1   explanation  here object  x  alone increment the counter variable from 0 to 1 by not object y  But result it as  static counter

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dataclass definitions provide class-level names that are used to define the instance variables and the initialization method    init      If you want class-level variable in  dataclass you should use typing ClassVar type hint  The ClassVar type s parameters define the class-level variable s type  from typing import ClassVar from dataclasses import dataclass   dataclass class Test      i  ClassVar int    10     x  int     y  int          def   repr   self           return f quot Test  self x     self y     Test i    quot   Usage examples   gt  test1   Test 5  6   gt  test2   Test 10  11    gt  test1 Test self x 5  self y 6  Test i 10   gt  test2 Test self x 10  self y 11  Test i 10

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The best way I found is to use another class  You can create an object and then use it on other objects   class staticFlag      def   init   self           self   success   False     def isSuccess self           return self   success     def succeed self           self   success   True  class tryIt      def   init   self  staticFlag           self isSuccess   staticFlag isSuccess         self succeed   staticFlag succeed  tryArr      flag   staticFlag   for i in range 10       tryArr append tryIt flag       if i    5          tryArr i  succeed       print tryArr i  isSuccess     With the example above  I made a class named staticFlag   This class should present the static var   success  Private Static Var    tryIt class represented the regular class we need to use   Now I made an object for one flag  staticFlag   This flag will be sent as reference to all the regular objects   All these objects are being added to the list tryArr     This Script Results   False False False False False True True True True True

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One very interesting point about Python s attribute lookup is that it can be used to create  virtual variables    class A object      label  Amazing     def   init   self d          self data d    def say self          print   s  s    self label self data    class B A     label  Bold     overrides A label  A 5  say          Amazing 5  B 3  say          Bold 3    Normally there aren t any assignments to these after they are created   Note that the lookup uses self because  although label is static in the sense of not being associated with a particular instance  the value still depends on the  class of the  instance

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Static Variables in Class factory python3 6 For anyone using a class factory with python3 6 and up use the nonlocal keyword to add it to the scope   context of the class being created like so   gt  gt  gt  def SomeFactory some var None           class SomeClass object               nonlocal some var             def print                    print some var          return SomeClass       gt  gt  gt  SomeFactory some var  quot hello world quot   print   hello world

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You could also enforce a class to be static using metaclass   class StaticClassError Exception       pass   class StaticClass        metaclass     abc ABCMeta      def   new   cls   args    kw           raise StaticClassError   s is a static class and cannot be initiated                                     cls   class MyClass StaticClass       a   1     b   3       staticmethod     def add x  y           return x y   Then whenever by accident you try to initialize MyClass you ll get an StaticClassError

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Not like the  staticmethod but class variables are static method of class and are shared with all the instances  Now you can access it like instance   MyClass   print instance i   or print MyClass i   you have to assign the value to these variables I was trying class MyClass    i  str  and assigning the value in one method call  in that case it will not work and will throw an error i is not attribute of MyClass

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When define some member variable outside any member method  the variable can be either static or non-static depending on how the variable is expressed     CLASSNAME var is static variable INSTANCENAME var is not static variable   self var inside class is not static variable   var inside the class member function is not defined    For example      usr bin python  class A      var 1      def printvar self           print  self var is  d    self var         print  A var is  d    A var       a   A       a var   2     a printvar        A var   3     a printvar     The results are  self var is 2 A var is 1 self var is 2 A var is 3

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Blair Conrad said static variables declared inside the class definition  but not inside a method are class or  static  variables    gt  gt  gt  class Test object           i   3      gt  gt  gt  Test i 3   There are a few gotcha s here  Carrying on from the example above    gt  gt  gt  t   Test    gt  gt  gt  t i        static  variable accessed via instance 3  gt  gt  gt  t i   5   but if we assign to the instance      gt  gt  gt  Test i    we have not changed the  static  variable 3  gt  gt  gt  t i       we have overwritten Test i on t by creating a new attribute t i 5  gt  gt  gt  Test i   6   to change the  static  variable we do it by assigning to the class  gt  gt  gt  t i 5  gt  gt  gt  Test i 6  gt  gt  gt  u   Test    gt  gt  gt  u i 6             changes to t do not affect new instances of Test    Namespaces are one honking great idea -- let s do more of those   gt  gt  gt  Test   dict     i   6        gt  gt  gt  t   dict     i   5   gt  gt  gt  u   dict        Notice how the instance variable t i got out of sync with the  static  class variable when the attribute i was set directly on t  This is because i was re-bound within the t namespace  which is distinct from the Test namespace  If you want to change the value of a  static  variable  you must change it within the scope  or object  where it was originally defined  I put  static  in quotes because Python does not really have static variables in the sense that C   and Java do   Although it doesn t say anything specific about static variables or methods  the Python tutorial has some relevant information on classes and class objects     Steve Johnson also answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class Test object        staticmethod     def f arg1  arg2                       beid also mentioned classmethod  which is similar to staticmethod  A classmethod s first argument is the class object  Example   class Test object       i   3   class  or static  variable      classmethod     def g cls  arg             here we can use  cls  instead of the class name  Test          if arg  gt  cls i              cls i   arg   would be the same as Test i   arg1

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To avoid any potential confusion  I would like to contrast static variables and immutable objects   Some primitive object types like integers  floats  strings  and touples are immutable in Python  This means that the object that is referred to by a given name cannot change if it is of one of the aforementioned object types  The name can be reassigned to a different object  but the object itself may not be changed   Making a variable static takes this a step further by disallowing the variable name to point to any object but that to which it currently points   Note  this is a general software concept and not specific to Python  please see others  posts for information about implementing statics in Python

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To avoid any potential confusion  I would like to contrast static variables and immutable objects   Some primitive object types like integers  floats  strings  and touples are immutable in Python  This means that the object that is referred to by a given name cannot change if it is of one of the aforementioned object types  The name can be reassigned to a different object  but the object itself may not be changed   Making a variable static takes this a step further by disallowing the variable name to point to any object but that to which it currently points   Note  this is a general software concept and not specific to Python  please see others  posts for information about implementing statics in Python

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In regards to this answer  for a constant static variable  you can use a descriptor  Here s an example   class ConstantAttribute object          You can initialize my value but not change it         def   init   self  value           self value   value      def   get   self  obj  type None           return self value      def   set   self  obj  val           pass   class Demo object       x   ConstantAttribute 10    class SubDemo Demo       x   10   demo   Demo   subdemo   SubDemo     should not change demo x   100   should change subdemo x   100 print  small demo   demo x print  small subdemo   subdemo x print  big demo   Demo x print  big subdemo   SubDemo x   resulting in      small demo 10 small subdemo 100 big demo 10 big subdemo 10   You can always raise an exception if quietly ignoring setting value  pass above  is not your thing  If you re looking for a C    Java style static class variable   class StaticAttribute object       def   init   self  value           self value   value      def   get   self  obj  type None           return self value      def   set   self  obj  val           self value   val   Have a look at this answer and the official docs HOWTO for more information about descriptors

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Static methods in python are called classmethods  Take a look at the following code  class MyClass       def myInstanceMethod self           print  output from an instance method        classmethod     def myStaticMethod cls           print  output from a static method    gt  gt  gt  MyClass myInstanceMethod   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unbound method myInstanceMethod   must be called         gt  gt  gt  MyClass myStaticMethod   output from a static method   Notice that when we call the method myInstanceMethod  we get an error  This is because it requires that method be called on an instance of this class  The method myStaticMethod is set as a classmethod using the decorator  classmethod   Just for kicks and giggles  we could call myInstanceMethod on the class by passing in an instance of the class  like so    gt  gt  gt  MyClass myInstanceMethod MyClass    output from an instance method

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Variables declared inside the class definition  but not inside a method are class or static variables    gt  gt  gt  class MyClass          i   3      gt  gt  gt  MyClass i 3    As  millerdev points out  this creates a class-level i variable  but this is distinct from any instance-level i variable  so you could have   gt  gt  gt  m   MyClass    gt  gt  gt  m i   4  gt  gt  gt  MyClass i  m i  gt  gt  gt   3  4    This is different from C   and Java  but not so different from C   where a static member can t be accessed using a reference to an instance   See what the Python tutorial has to say on the subject of classes and class objects    Steve Johnson has already answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class C       staticmethod     def f arg1  arg2               beidy recommends classmethods over staticmethod  as the method then receives the class type as the first argument  but I m still a little fuzzy on the advantages of this approach over staticmethod  If you are too  then it probably doesn t matter

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The best way I found is to use another class  You can create an object and then use it on other objects   class staticFlag      def   init   self           self   success   False     def isSuccess self           return self   success     def succeed self           self   success   True  class tryIt      def   init   self  staticFlag           self isSuccess   staticFlag isSuccess         self succeed   staticFlag succeed  tryArr      flag   staticFlag   for i in range 10       tryArr append tryIt flag       if i    5          tryArr i  succeed       print tryArr i  isSuccess     With the example above  I made a class named staticFlag   This class should present the static var   success  Private Static Var    tryIt class represented the regular class we need to use   Now I made an object for one flag  staticFlag   This flag will be sent as reference to all the regular objects   All these objects are being added to the list tryArr     This Script Results   False False False False False True True True True True

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One very interesting point about Python s attribute lookup is that it can be used to create  virtual variables    class A object      label  Amazing     def   init   self d          self data d    def say self          print   s  s    self label self data    class B A     label  Bold     overrides A label  A 5  say          Amazing 5  B 3  say          Bold 3    Normally there aren t any assignments to these after they are created   Note that the lookup uses self because  although label is static in the sense of not being associated with a particular instance  the value still depends on the  class of the  instance

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So this is probably a hack  but I ve been using eval str  to obtain an static object  kind of a contradiction  in python 3   There is an Records py file that has nothing but class objects defined with static methods and constructors that save some arguments   Then from another  py file I import Records but i need to dynamically select each object and then instantiate it on demand according to the type of data being read in   So where object name    RecordOne  or the class name  I call cur type   eval object name  and then to instantiate it you do cur inst   cur type args  However before you instantiate you can call static methods from cur type getName   for example  kind of like abstract base class implementation or whatever the goal is   However in the backend  it s probably instantiated in python and is not truly static  because eval is returning an object    which must have been instantiated    that gives static like behavior

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Variables declared inside the class definition  but not inside a method are class or static variables    gt  gt  gt  class MyClass          i   3      gt  gt  gt  MyClass i 3    As  millerdev points out  this creates a class-level i variable  but this is distinct from any instance-level i variable  so you could have   gt  gt  gt  m   MyClass    gt  gt  gt  m i   4  gt  gt  gt  MyClass i  m i  gt  gt  gt   3  4    This is different from C   and Java  but not so different from C   where a static member can t be accessed using a reference to an instance   See what the Python tutorial has to say on the subject of classes and class objects    Steve Johnson has already answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class C       staticmethod     def f arg1  arg2               beidy recommends classmethods over staticmethod  as the method then receives the class type as the first argument  but I m still a little fuzzy on the advantages of this approach over staticmethod  If you are too  then it probably doesn t matter

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Static and Class Methods  As the other answers have noted  static and class methods are easily accomplished using the built-in decorators   class Test object          regular instance method      def MyMethod self           pass        class method       classmethod     def MyClassMethod klass           pass        static method       staticmethod     def MyStaticMethod            pass   As usual  the first argument to MyMethod   is bound to the class instance object  In contrast  the first argument to MyClassMethod   is bound to the class object itself  e g   in this case  Test   For MyStaticMethod    none of the arguments are bound  and having arguments at all is optional     Static Variables   However  implementing  static variables   well  mutable static variables  anyway  if that s not a contradiction in terms     is not as straight forward  As millerdev pointed out in his answer  the problem is that Python s class attributes are not truly  static variables   Consider    class Test object       i   3    This is a class attribute  x   Test   x i   12     Attempt to change the value of the class attribute using x instance assert x i    Test i    ERROR assert Test i    3      Test i was not affected assert x i    12        x i is a different object than Test i   This is because the line x i   12 has added a new instance attribute i to x instead of changing the value of the Test class i attribute    Partial expected static variable behavior  i e   syncing of the attribute between multiple instances  but not with the class itself  see  gotcha  below   can be achieved by turning the class attribute into a property   class Test object         i   3       property     def i self           return type self   i       i setter     def i self val           type self   i   val     ALTERNATIVE IMPLEMENTATION - FUNCTIONALLY EQUIVALENT TO ABOVE        except with separate methods for getting and setting i      class Test object         i   3      def get i self           return type self   i      def set i self val           type self   i   val      i   property get i  set i    Now you can do   x1   Test   x2   Test   x1 i   50 assert x2 i    x1 i    no error assert x2 i    50      the property is synced   The static variable will now remain in sync between all class instances     NOTE  That is  unless a class instance decides to define its own version of  i  But if someone decides to do THAT  they deserve what they get  don t they      Note that technically speaking  i is still not a  static variable  at all  it is a property  which is a special type of descriptor  However  the property behavior is now equivalent to a  mutable  static variable synced across all class instances    Immutable  Static Variables   For immutable static variable behavior  simply omit the property setter   class Test object         i   3       property     def i self           return type self   i     ALTERNATIVE IMPLEMENTATION - FUNCTIONALLY EQUIVALENT TO ABOVE        except with separate methods for getting i      class Test object         i   3      def get i self           return type self   i      i   property get i    Now attempting to set the instance i attribute will return an AttributeError    x   Test   assert x i    3    success x i   12           ERROR   One Gotcha to be Aware of  Note that the above methods only work with instances of your class - they will not work when using the class itself  So for example    x   Test   assert x i    Test i    ERROR    x i and Test i are two different objects  type Test i     class  property  type x i        class  int    The line assert Test i    x i produces an error  because the i attribute of Test and x are two different objects    Many people will find this surprising  However  it should not be  If we go back and inspect our Test class definition  the second version   we take note of this line        i   property get i     Clearly  the member i of Test must be a property object  which is the type of object returned from the property function    If you find the above confusing  you are most likely still thinking about it from the perspective of other languages  e g  Java or c     You should go study the property object  about the order in which Python attributes are returned  the descriptor protocol  and the method resolution order  MRO     I present a solution to the above  gotcha  below  however I would suggest - strenuously - that you do not try to do something like the following until - at minimum - you thoroughly understand why assert Test i   x i causes an error    REAL  ACTUAL Static Variables - Test i    x i  I present the  Python 3  solution below for informational purposes only  I am not endorsing it as a  good solution   I have my doubts as to whether emulating the static variable behavior of other languages in Python is ever actually necessary  However  regardless as to whether it is actually useful  the below should help further understanding of how Python works    UPDATE  this attempt is really pretty awful  if you insist on doing something like this  hint  please don t  Python is a very elegant language and shoe-horning it into behaving like another language is just not necessary   use the code in Ethan Furman s answer instead   Emulating static variable behavior of other languages using a metaclass  A metaclass is the class of a class  The default metaclass for all classes in Python  i e   the  new style  classes post Python 2 3 I believe  is type  For example    type int     class  type  type str     class  type  class Test    pass type Test    class  type    However  you can define your own metaclass like this    class MyMeta type   pass   And apply it to your own class like this  Python 3 only    class MyClass metaclass   MyMeta       pass  type MyClass     class MyMeta   Below is a metaclass I have created which attempts to emulate  static variable  behavior of other languages  It basically works by replacing the default getter  setter  and deleter with versions which check to see if the attribute being requested is a  static variable     A catalog of the  static variables  is stored in the StaticVarMeta statics attribute  All attribute requests are initially attempted to be resolved using a substitute resolution order  I have dubbed this the  static resolution order   or  SRO   This is done by looking for the requested attribute in the set of  static variables  for a given class  or its parent classes   If the attribute does not appear in the  SRO   the class will fall back on the default attribute get set delete behavior  i e    MRO      from functools import wraps  class StaticVarsMeta type          A metaclass for creating classes that emulate the  static variable  behavior     of other languages  I do not advise actually using this for anything         Behavior is intended to be similar to classes that use   slots    However   normal      attributes and   statics    can coexist  unlike with   slots           Example usage            class MyBaseClass metaclass   StaticVarsMeta                 statics       a   b   c               i   0    regular attribute             a   1    static var defined  optional           class MyParentClass MyBaseClass                 statics       d   e   f               j   2                regular attribute             d  e  f   3  4  5    Static vars             a  b  c   6  7  8    Static vars  inherited from MyBaseClass  defined re-defined here           class MyChildClass MyParentClass                 statics       a   b   c               j   2    regular attribute  redefines j from MyParentClass              d  e  f   9  10  11     Static vars  inherited from MyParentClass  redefined here              a  b  c   12  13  14    Static vars  overriding previous definition in MyParentClass here         statics          def   new   mcls  name  bases  namespace             Get the class object         cls   super     new   mcls  name  bases  namespace            Establish the  statics resolution order          cls   sro     tuple c for c in cls   mro   if isinstance c mcls              Replace class getter  setter  and deleter for instance attributes         cls   getattribute     StaticVarsMeta   inst getattribute   cls  cls   getattribute            cls   setattr     StaticVarsMeta   inst setattr   cls  cls   setattr            cls   delattr     StaticVarsMeta   inst delattr   cls  cls   delattr              Store the list of static variables for the class object           This list is permanent and cannot be changed  similar to   slots           try              mcls statics cls    getattr cls    statics             except AttributeError              mcls statics cls    namespace    statics       set     No static vars provided           Check and make sure the statics var names are strings         if any not isinstance static str  for static in mcls statics cls                typ   dict zip  not isinstance static str  for static in mcls statics cls    map type mcls statics cls     True    name               raise TypeError    statics   items must be strings  not  0   format typ             Move any previously existing  not overridden statics to the static var parent class es          if len cls   sro     gt  1              for attr value in namespace items                    if attr not in StaticVarsMeta statics cls  and attr        statics                          for c in cls   sro   1                            if attr in StaticVarsMeta statics c                               setattr c attr value                              delattr cls attr          return cls     def   inst getattribute   self  orig getattribute              Replaces the class   getattribute               wraps orig getattribute          def wrapper self  attr               if StaticVarsMeta is static type self  attr                   return StaticVarsMeta   getstatic   type self  attr              else                  return orig getattribute self  attr          return wrapper     def   inst setattr   self  orig setattribute              Replaces the class   setattr               wraps orig setattribute          def wrapper self  attr  value               if StaticVarsMeta is static type self  attr                   StaticVarsMeta   setstatic   type self  attr  value              else                  orig setattribute self  attr  value          return wrapper     def   inst delattr   self  orig delattribute              Replaces the class   delattr               wraps orig delattribute          def wrapper self  attr               if StaticVarsMeta is static type self  attr                   StaticVarsMeta   delstatic   type self  attr              else                  orig delattribute self  attr          return wrapper     def   getstatic   cls attr              Static variable getter            for c in cls   sro                if attr in StaticVarsMeta statics c                   try                      return getattr c attr                  except AttributeError                      pass         raise AttributeError cls   name       object has no attribute   0    format attr       def   setstatic   cls attr value              Static variable setter            for c in cls   sro                if attr in StaticVarsMeta statics c                   setattr c attr value                  break     def   delstatic   cls attr              Static variable deleter            for c in cls   sro                if attr in StaticVarsMeta statics c                   try                      delattr c attr                      break                 except AttributeError                      pass         raise AttributeError cls   name       object has no attribute   0    format attr       def   delattr   cls attr              Prevent   sro   attribute from deletion            if attr       sro                 raise AttributeError  readonly attribute           super     delattr   attr      def is static cls attr              Returns True if an attribute is a static variable of any class in the   sro              if any attr in StaticVarsMeta statics c  for c in cls   sro                 return True         return False

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Absolutely Yes    Python by itself don t have any static data member explicitly  but We can have by doing so   class A      counter  0     def callme  self           A counter   1     def getcount  self           return self counter    gt  gt  gt  x A    gt  gt  gt  y A    gt  gt  gt  print x getcount     gt  gt  gt  print y getcount     gt  gt  gt  x callme     gt  gt  gt  print x getcount     gt  gt  gt  print y getcount      output  0 0 1 1   explanation  here object  x  alone increment the counter variable from 0 to 1 by not object y  But result it as  static counter

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It is possible to have static class variables  but probably not worth the effort   Here s a proof-of-concept written in Python 3 -- if any of the exact details are wrong the code can be tweaked to match just about whatever you mean by a static variable     class Static      def   init   self  value  doc None           self deleted   False         self value   value         self   doc     doc     def   get   self  inst  cls None           if self deleted              raise AttributeError  Attribute not set           return self value     def   set   self  inst  value           self deleted   False         self value   value     def   delete   self  inst           self deleted   True  class StaticType type       def   delattr   cls  name           obj   cls   dict   get name          if isinstance obj  Static               obj   delete   name          else              super StaticType  cls    delattr   name      def   getattribute   cls   args           obj   super StaticType  cls    getattribute    args          if isinstance obj  Static               obj   obj   get   cls  cls   class            return obj     def   setattr   cls  name  val             check if object already exists         obj   cls   dict   get name          if isinstance obj  Static               obj   set   name  val          else              super StaticType  cls    setattr   name  val    and in use   class MyStatic metaclass StaticType               Testing static vars             a   Static 9      b   Static 12      c   3  class YourStatic MyStatic       d   Static  woo hoo       e   Static  doo wop     and some tests   ms1   MyStatic   ms2   MyStatic   ms3   MyStatic   assert ms1 a    ms2 a    ms3 a    MyStatic a assert ms1 b    ms2 b    ms3 b    MyStatic b assert ms1 c    ms2 c    ms3 c    MyStatic c ms1 a   77 assert ms1 a    ms2 a    ms3 a    MyStatic a ms2 b   99 assert ms1 b    ms2 b    ms3 b    MyStatic b MyStatic a   101 assert ms1 a    ms2 a    ms3 a    MyStatic a MyStatic b   139 assert ms1 b    ms2 b    ms3 b    MyStatic b del MyStatic b for inst in  ms1  ms2  ms3       try          getattr inst   b       except AttributeError          pass     else          print  AttributeError not raised on  r    attr  ms1 c   13 ms2 c   17 ms3 c   19 assert ms1 c    13 assert ms2 c    17 assert ms3 c    19 MyStatic c   43 assert ms1 c    13 assert ms2 c    17 assert ms3 c    19  ys1   YourStatic   ys2   YourStatic   ys3   YourStatic   MyStatic b    burgler  assert ys1 a    ys2 a    ys3 a    YourStatic a    MyStatic a assert ys1 b    ys2 b    ys3 b    YourStatic b    MyStatic b assert ys1 d    ys2 d    ys3 d    YourStatic d assert ys1 e    ys2 e    ys3 e    YourStatic e ys1 a    blah  assert ys1 a    ys2 a    ys3 a    YourStatic a    MyStatic a ys2 b    kelp  assert ys1 b    ys2 b    ys3 b    YourStatic b    MyStatic b ys1 d    fee  assert ys1 d    ys2 d    ys3 d    YourStatic d ys2 e    fie  assert ys1 e    ys2 e    ys3 e    YourStatic e MyStatic a    aargh  assert ys1 a    ys2 a    ys3 a    YourStatic a    MyStatic a

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In regards to this answer  for a constant static variable  you can use a descriptor  Here s an example   class ConstantAttribute object          You can initialize my value but not change it         def   init   self  value           self value   value      def   get   self  obj  type None           return self value      def   set   self  obj  val           pass   class Demo object       x   ConstantAttribute 10    class SubDemo Demo       x   10   demo   Demo   subdemo   SubDemo     should not change demo x   100   should change subdemo x   100 print  small demo   demo x print  small subdemo   subdemo x print  big demo   Demo x print  big subdemo   SubDemo x   resulting in      small demo 10 small subdemo 100 big demo 10 big subdemo 10   You can always raise an exception if quietly ignoring setting value  pass above  is not your thing  If you re looking for a C    Java style static class variable   class StaticAttribute object       def   init   self  value           self value   value      def   get   self  obj  type None           return self value      def   set   self  obj  val           self value   val   Have a look at this answer and the official docs HOWTO for more information about descriptors

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You can use a list or a dictionary to get  static behavior  between instances   class Fud        class vars     origin open  False        def   init   self  origin   True            self origin   origin          self opened   True          if origin               self class vars  origin open     True        def make another fud self                Generating another Fud   from the origin instance               return Fud False         def close self            self opened   False          if self origin               self class vars  origin open     False   fud1   Fud   fud2   fud1 make another fud    print  f is this the original fud   fud2 origin    print  f is the original fud open   fud2 class vars  origin open        is this the original fud  False   is the original fud open  True  fud1 close    print  f is the original fud open   fud2 class vars  origin open        is the original fud open  False

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Blair Conrad said static variables declared inside the class definition  but not inside a method are class or  static  variables    gt  gt  gt  class Test object           i   3      gt  gt  gt  Test i 3   There are a few gotcha s here  Carrying on from the example above    gt  gt  gt  t   Test    gt  gt  gt  t i        static  variable accessed via instance 3  gt  gt  gt  t i   5   but if we assign to the instance      gt  gt  gt  Test i    we have not changed the  static  variable 3  gt  gt  gt  t i       we have overwritten Test i on t by creating a new attribute t i 5  gt  gt  gt  Test i   6   to change the  static  variable we do it by assigning to the class  gt  gt  gt  t i 5  gt  gt  gt  Test i 6  gt  gt  gt  u   Test    gt  gt  gt  u i 6             changes to t do not affect new instances of Test    Namespaces are one honking great idea -- let s do more of those   gt  gt  gt  Test   dict     i   6        gt  gt  gt  t   dict     i   5   gt  gt  gt  u   dict        Notice how the instance variable t i got out of sync with the  static  class variable when the attribute i was set directly on t  This is because i was re-bound within the t namespace  which is distinct from the Test namespace  If you want to change the value of a  static  variable  you must change it within the scope  or object  where it was originally defined  I put  static  in quotes because Python does not really have static variables in the sense that C   and Java do   Although it doesn t say anything specific about static variables or methods  the Python tutorial has some relevant information on classes and class objects     Steve Johnson also answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class Test object        staticmethod     def f arg1  arg2                       beid also mentioned classmethod  which is similar to staticmethod  A classmethod s first argument is the class object  Example   class Test object       i   3   class  or static  variable      classmethod     def g cls  arg             here we can use  cls  instead of the class name  Test          if arg  gt  cls i              cls i   arg   would be the same as Test i   arg1

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Blair Conrad said static variables declared inside the class definition  but not inside a method are class or  static  variables    gt  gt  gt  class Test object           i   3      gt  gt  gt  Test i 3   There are a few gotcha s here  Carrying on from the example above    gt  gt  gt  t   Test    gt  gt  gt  t i        static  variable accessed via instance 3  gt  gt  gt  t i   5   but if we assign to the instance      gt  gt  gt  Test i    we have not changed the  static  variable 3  gt  gt  gt  t i       we have overwritten Test i on t by creating a new attribute t i 5  gt  gt  gt  Test i   6   to change the  static  variable we do it by assigning to the class  gt  gt  gt  t i 5  gt  gt  gt  Test i 6  gt  gt  gt  u   Test    gt  gt  gt  u i 6             changes to t do not affect new instances of Test    Namespaces are one honking great idea -- let s do more of those   gt  gt  gt  Test   dict     i   6        gt  gt  gt  t   dict     i   5   gt  gt  gt  u   dict        Notice how the instance variable t i got out of sync with the  static  class variable when the attribute i was set directly on t  This is because i was re-bound within the t namespace  which is distinct from the Test namespace  If you want to change the value of a  static  variable  you must change it within the scope  or object  where it was originally defined  I put  static  in quotes because Python does not really have static variables in the sense that C   and Java do   Although it doesn t say anything specific about static variables or methods  the Python tutorial has some relevant information on classes and class objects     Steve Johnson also answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class Test object        staticmethod     def f arg1  arg2                       beid also mentioned classmethod  which is similar to staticmethod  A classmethod s first argument is the class object  Example   class Test object       i   3   class  or static  variable      classmethod     def g cls  arg             here we can use  cls  instead of the class name  Test          if arg  gt  cls i              cls i   arg   would be the same as Test i   arg1

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Yes  definitely possible to write static variables and methods in python   Static Variables   Variable declared at class level are called static variable which can be accessed directly using class name        gt  gt  gt  class A             my var    shagun        gt  gt  gt  print A my var          shagun   Instance variables  Variables that are related and accessed by instance of a class are instance variables       gt  gt  gt  a   A       gt  gt  gt  a my var    pruthi      gt  gt  gt  print A my var a my var         shagun pruthi   Static Methods  Similar to variables  static methods can be accessed directly using class Name  No need to create an instance    But keep in mind  a static method cannot call a non-static method in python        gt  gt  gt  class A              staticmethod            def my static method                       print  Yippey                 gt  gt  gt  A my static method      Yippey

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You can also add class variables to classes on the fly   gt  gt  gt  class X          pass       gt  gt  gt  X bar   0  gt  gt  gt  x   X    gt  gt  gt  x bar 0  gt  gt  gt  x foo Traceback  most recent call last     File   lt interactive input gt    line 1  in  lt module gt  AttributeError  X instance has no attribute  foo   gt  gt  gt  X foo   1  gt  gt  gt  x foo 1   And class instances can change class variables  class X    l        def   init   self       self l append 1   print X   l print X   l   gt python test py  1   1  1

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Static methods in python are called classmethods  Take a look at the following code  class MyClass       def myInstanceMethod self           print  output from an instance method        classmethod     def myStaticMethod cls           print  output from a static method    gt  gt  gt  MyClass myInstanceMethod   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unbound method myInstanceMethod   must be called         gt  gt  gt  MyClass myStaticMethod   output from a static method   Notice that when we call the method myInstanceMethod  we get an error  This is because it requires that method be called on an instance of this class  The method myStaticMethod is set as a classmethod using the decorator  classmethod   Just for kicks and giggles  we could call myInstanceMethod on the class by passing in an instance of the class  like so    gt  gt  gt  MyClass myInstanceMethod MyClass    output from an instance method

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Personally I would use a classmethod whenever I needed a static method  Mainly because I get the class as an argument   class myObj object      def myMethod cls              myMethod   classmethod myMethod     or use a decorator  class myObj object       classmethod    def myMethod cls    For static properties   Its time you look up some python definition   variable can always change  There are two types of them mutable and immutable   Also  there are class attributes and instance attributes   Nothing really like static attributes in the sense of java  amp  c    Why use static method in pythonic sense  if it has no relation whatever to the class  If I were you  I d either use classmethod or define the method independent from the class

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Yes  definitely possible to write static variables and methods in python   Static Variables   Variable declared at class level are called static variable which can be accessed directly using class name        gt  gt  gt  class A             my var    shagun        gt  gt  gt  print A my var          shagun   Instance variables  Variables that are related and accessed by instance of a class are instance variables       gt  gt  gt  a   A       gt  gt  gt  a my var    pruthi      gt  gt  gt  print A my var a my var         shagun pruthi   Static Methods  Similar to variables  static methods can be accessed directly using class Name  No need to create an instance    But keep in mind  a static method cannot call a non-static method in python        gt  gt  gt  class A              staticmethod            def my static method                       print  Yippey                 gt  gt  gt  A my static method      Yippey

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If you are attempting to share a static variable for  by example  increasing it across other instances  something like this script works fine     - - coding  utf-8 - - class Worker      id   1      def   init   self           self name              self document              self id   Worker id         Worker id    1      def   str   self           return u    -        format self id  self name  self document  encode  utf8     class Workers      def   init   self           self list           def add self  name  doc           worker   Worker           worker name   name         worker document   doc         self list append worker    if   name         main         workers   Workers       for item in    Fiona    0009898      Maria    66328191      Sandra    2342184      Elvira    425872             workers add item 0   item 1       for worker in workers list          print worker      print  next id   i    Worker id

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You could also enforce a class to be static using metaclass   class StaticClassError Exception       pass   class StaticClass        metaclass     abc ABCMeta      def   new   cls   args    kw           raise StaticClassError   s is a static class and cannot be initiated                                     cls   class MyClass StaticClass       a   1     b   3       staticmethod     def add x  y           return x y   Then whenever by accident you try to initialize MyClass you ll get an StaticClassError

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Blair Conrad said static variables declared inside the class definition  but not inside a method are class or  static  variables    gt  gt  gt  class Test object           i   3      gt  gt  gt  Test i 3   There are a few gotcha s here  Carrying on from the example above    gt  gt  gt  t   Test    gt  gt  gt  t i        static  variable accessed via instance 3  gt  gt  gt  t i   5   but if we assign to the instance      gt  gt  gt  Test i    we have not changed the  static  variable 3  gt  gt  gt  t i       we have overwritten Test i on t by creating a new attribute t i 5  gt  gt  gt  Test i   6   to change the  static  variable we do it by assigning to the class  gt  gt  gt  t i 5  gt  gt  gt  Test i 6  gt  gt  gt  u   Test    gt  gt  gt  u i 6             changes to t do not affect new instances of Test    Namespaces are one honking great idea -- let s do more of those   gt  gt  gt  Test   dict     i   6        gt  gt  gt  t   dict     i   5   gt  gt  gt  u   dict        Notice how the instance variable t i got out of sync with the  static  class variable when the attribute i was set directly on t  This is because i was re-bound within the t namespace  which is distinct from the Test namespace  If you want to change the value of a  static  variable  you must change it within the scope  or object  where it was originally defined  I put  static  in quotes because Python does not really have static variables in the sense that C   and Java do   Although it doesn t say anything specific about static variables or methods  the Python tutorial has some relevant information on classes and class objects     Steve Johnson also answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class Test object        staticmethod     def f arg1  arg2                       beid also mentioned classmethod  which is similar to staticmethod  A classmethod s first argument is the class object  Example   class Test object       i   3   class  or static  variable      classmethod     def g cls  arg             here we can use  cls  instead of the class name  Test          if arg  gt  cls i              cls i   arg   would be the same as Test i   arg1

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You can also add class variables to classes on the fly   gt  gt  gt  class X          pass       gt  gt  gt  X bar   0  gt  gt  gt  x   X    gt  gt  gt  x bar 0  gt  gt  gt  x foo Traceback  most recent call last     File   lt interactive input gt    line 1  in  lt module gt  AttributeError  X instance has no attribute  foo   gt  gt  gt  X foo   1  gt  gt  gt  x foo 1   And class instances can change class variables  class X    l        def   init   self       self l append 1   print X   l print X   l   gt python test py  1   1  1

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Static Variables in Class factory python3 6 For anyone using a class factory with python3 6 and up use the nonlocal keyword to add it to the scope   context of the class being created like so   gt  gt  gt  def SomeFactory some var None           class SomeClass object               nonlocal some var             def print                    print some var          return SomeClass       gt  gt  gt  SomeFactory some var  quot hello world quot   print   hello world

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When define some member variable outside any member method  the variable can be either static or non-static depending on how the variable is expressed     CLASSNAME var is static variable INSTANCENAME var is not static variable   self var inside class is not static variable   var inside the class member function is not defined    For example      usr bin python  class A      var 1      def printvar self           print  self var is  d    self var         print  A var is  d    A var       a   A       a var   2     a printvar        A var   3     a printvar     The results are  self var is 2 A var is 1 self var is 2 A var is 3

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To avoid any potential confusion  I would like to contrast static variables and immutable objects   Some primitive object types like integers  floats  strings  and touples are immutable in Python  This means that the object that is referred to by a given name cannot change if it is of one of the aforementioned object types  The name can be reassigned to a different object  but the object itself may not be changed   Making a variable static takes this a step further by disallowing the variable name to point to any object but that to which it currently points   Note  this is a general software concept and not specific to Python  please see others  posts for information about implementing statics in Python

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Personally I would use a classmethod whenever I needed a static method  Mainly because I get the class as an argument   class myObj object      def myMethod cls              myMethod   classmethod myMethod     or use a decorator  class myObj object       classmethod    def myMethod cls    For static properties   Its time you look up some python definition   variable can always change  There are two types of them mutable and immutable   Also  there are class attributes and instance attributes   Nothing really like static attributes in the sense of java  amp  c    Why use static method in pythonic sense  if it has no relation whatever to the class  If I were you  I d either use classmethod or define the method independent from the class

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Personally I would use a classmethod whenever I needed a static method  Mainly because I get the class as an argument   class myObj object      def myMethod cls              myMethod   classmethod myMethod     or use a decorator  class myObj object       classmethod    def myMethod cls    For static properties   Its time you look up some python definition   variable can always change  There are two types of them mutable and immutable   Also  there are class attributes and instance attributes   Nothing really like static attributes in the sense of java  amp  c    Why use static method in pythonic sense  if it has no relation whatever to the class  If I were you  I d either use classmethod or define the method independent from the class

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You can also add class variables to classes on the fly   gt  gt  gt  class X          pass       gt  gt  gt  X bar   0  gt  gt  gt  x   X    gt  gt  gt  x bar 0  gt  gt  gt  x foo Traceback  most recent call last     File   lt interactive input gt    line 1  in  lt module gt  AttributeError  X instance has no attribute  foo   gt  gt  gt  X foo   1  gt  gt  gt  x foo 1   And class instances can change class variables  class X    l        def   init   self       self l append 1   print X   l print X   l   gt python test py  1   1  1

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One special thing to note about static properties  amp  instance properties  shown in the example below   class my cls    my prop   0   static property print my cls my prop   -- gt  0   assign value to static property my cls my prop   1  print my cls my prop   -- gt  1   access static property thru  instance my inst   my cls   print my inst my prop  -- gt  1   instance property is different from static property   after being assigned a value my inst my prop   2 print my cls my prop   -- gt  1 print my inst my prop  -- gt  2   This means before assigning the value to instance property  if we try to access the property thru  instance  the static value is used  Each property declared in python class always has a static slot in memory

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Static and Class Methods  As the other answers have noted  static and class methods are easily accomplished using the built-in decorators   class Test object          regular instance method      def MyMethod self           pass        class method       classmethod     def MyClassMethod klass           pass        static method       staticmethod     def MyStaticMethod            pass   As usual  the first argument to MyMethod   is bound to the class instance object  In contrast  the first argument to MyClassMethod   is bound to the class object itself  e g   in this case  Test   For MyStaticMethod    none of the arguments are bound  and having arguments at all is optional     Static Variables   However  implementing  static variables   well  mutable static variables  anyway  if that s not a contradiction in terms     is not as straight forward  As millerdev pointed out in his answer  the problem is that Python s class attributes are not truly  static variables   Consider    class Test object       i   3    This is a class attribute  x   Test   x i   12     Attempt to change the value of the class attribute using x instance assert x i    Test i    ERROR assert Test i    3      Test i was not affected assert x i    12        x i is a different object than Test i   This is because the line x i   12 has added a new instance attribute i to x instead of changing the value of the Test class i attribute    Partial expected static variable behavior  i e   syncing of the attribute between multiple instances  but not with the class itself  see  gotcha  below   can be achieved by turning the class attribute into a property   class Test object         i   3       property     def i self           return type self   i       i setter     def i self val           type self   i   val     ALTERNATIVE IMPLEMENTATION - FUNCTIONALLY EQUIVALENT TO ABOVE        except with separate methods for getting and setting i      class Test object         i   3      def get i self           return type self   i      def set i self val           type self   i   val      i   property get i  set i    Now you can do   x1   Test   x2   Test   x1 i   50 assert x2 i    x1 i    no error assert x2 i    50      the property is synced   The static variable will now remain in sync between all class instances     NOTE  That is  unless a class instance decides to define its own version of  i  But if someone decides to do THAT  they deserve what they get  don t they      Note that technically speaking  i is still not a  static variable  at all  it is a property  which is a special type of descriptor  However  the property behavior is now equivalent to a  mutable  static variable synced across all class instances    Immutable  Static Variables   For immutable static variable behavior  simply omit the property setter   class Test object         i   3       property     def i self           return type self   i     ALTERNATIVE IMPLEMENTATION - FUNCTIONALLY EQUIVALENT TO ABOVE        except with separate methods for getting i      class Test object         i   3      def get i self           return type self   i      i   property get i    Now attempting to set the instance i attribute will return an AttributeError    x   Test   assert x i    3    success x i   12           ERROR   One Gotcha to be Aware of  Note that the above methods only work with instances of your class - they will not work when using the class itself  So for example    x   Test   assert x i    Test i    ERROR    x i and Test i are two different objects  type Test i     class  property  type x i        class  int    The line assert Test i    x i produces an error  because the i attribute of Test and x are two different objects    Many people will find this surprising  However  it should not be  If we go back and inspect our Test class definition  the second version   we take note of this line        i   property get i     Clearly  the member i of Test must be a property object  which is the type of object returned from the property function    If you find the above confusing  you are most likely still thinking about it from the perspective of other languages  e g  Java or c     You should go study the property object  about the order in which Python attributes are returned  the descriptor protocol  and the method resolution order  MRO     I present a solution to the above  gotcha  below  however I would suggest - strenuously - that you do not try to do something like the following until - at minimum - you thoroughly understand why assert Test i   x i causes an error    REAL  ACTUAL Static Variables - Test i    x i  I present the  Python 3  solution below for informational purposes only  I am not endorsing it as a  good solution   I have my doubts as to whether emulating the static variable behavior of other languages in Python is ever actually necessary  However  regardless as to whether it is actually useful  the below should help further understanding of how Python works    UPDATE  this attempt is really pretty awful  if you insist on doing something like this  hint  please don t  Python is a very elegant language and shoe-horning it into behaving like another language is just not necessary   use the code in Ethan Furman s answer instead   Emulating static variable behavior of other languages using a metaclass  A metaclass is the class of a class  The default metaclass for all classes in Python  i e   the  new style  classes post Python 2 3 I believe  is type  For example    type int     class  type  type str     class  type  class Test    pass type Test    class  type    However  you can define your own metaclass like this    class MyMeta type   pass   And apply it to your own class like this  Python 3 only    class MyClass metaclass   MyMeta       pass  type MyClass     class MyMeta   Below is a metaclass I have created which attempts to emulate  static variable  behavior of other languages  It basically works by replacing the default getter  setter  and deleter with versions which check to see if the attribute being requested is a  static variable     A catalog of the  static variables  is stored in the StaticVarMeta statics attribute  All attribute requests are initially attempted to be resolved using a substitute resolution order  I have dubbed this the  static resolution order   or  SRO   This is done by looking for the requested attribute in the set of  static variables  for a given class  or its parent classes   If the attribute does not appear in the  SRO   the class will fall back on the default attribute get set delete behavior  i e    MRO      from functools import wraps  class StaticVarsMeta type          A metaclass for creating classes that emulate the  static variable  behavior     of other languages  I do not advise actually using this for anything         Behavior is intended to be similar to classes that use   slots    However   normal      attributes and   statics    can coexist  unlike with   slots           Example usage            class MyBaseClass metaclass   StaticVarsMeta                 statics       a   b   c               i   0    regular attribute             a   1    static var defined  optional           class MyParentClass MyBaseClass                 statics       d   e   f               j   2                regular attribute             d  e  f   3  4  5    Static vars             a  b  c   6  7  8    Static vars  inherited from MyBaseClass  defined re-defined here           class MyChildClass MyParentClass                 statics       a   b   c               j   2    regular attribute  redefines j from MyParentClass              d  e  f   9  10  11     Static vars  inherited from MyParentClass  redefined here              a  b  c   12  13  14    Static vars  overriding previous definition in MyParentClass here         statics          def   new   mcls  name  bases  namespace             Get the class object         cls   super     new   mcls  name  bases  namespace            Establish the  statics resolution order          cls   sro     tuple c for c in cls   mro   if isinstance c mcls              Replace class getter  setter  and deleter for instance attributes         cls   getattribute     StaticVarsMeta   inst getattribute   cls  cls   getattribute            cls   setattr     StaticVarsMeta   inst setattr   cls  cls   setattr            cls   delattr     StaticVarsMeta   inst delattr   cls  cls   delattr              Store the list of static variables for the class object           This list is permanent and cannot be changed  similar to   slots           try              mcls statics cls    getattr cls    statics             except AttributeError              mcls statics cls    namespace    statics       set     No static vars provided           Check and make sure the statics var names are strings         if any not isinstance static str  for static in mcls statics cls                typ   dict zip  not isinstance static str  for static in mcls statics cls    map type mcls statics cls     True    name               raise TypeError    statics   items must be strings  not  0   format typ             Move any previously existing  not overridden statics to the static var parent class es          if len cls   sro     gt  1              for attr value in namespace items                    if attr not in StaticVarsMeta statics cls  and attr        statics                          for c in cls   sro   1                            if attr in StaticVarsMeta statics c                               setattr c attr value                              delattr cls attr          return cls     def   inst getattribute   self  orig getattribute              Replaces the class   getattribute               wraps orig getattribute          def wrapper self  attr               if StaticVarsMeta is static type self  attr                   return StaticVarsMeta   getstatic   type self  attr              else                  return orig getattribute self  attr          return wrapper     def   inst setattr   self  orig setattribute              Replaces the class   setattr               wraps orig setattribute          def wrapper self  attr  value               if StaticVarsMeta is static type self  attr                   StaticVarsMeta   setstatic   type self  attr  value              else                  orig setattribute self  attr  value          return wrapper     def   inst delattr   self  orig delattribute              Replaces the class   delattr               wraps orig delattribute          def wrapper self  attr               if StaticVarsMeta is static type self  attr                   StaticVarsMeta   delstatic   type self  attr              else                  orig delattribute self  attr          return wrapper     def   getstatic   cls attr              Static variable getter            for c in cls   sro                if attr in StaticVarsMeta statics c                   try                      return getattr c attr                  except AttributeError                      pass         raise AttributeError cls   name       object has no attribute   0    format attr       def   setstatic   cls attr value              Static variable setter            for c in cls   sro                if attr in StaticVarsMeta statics c                   setattr c attr value                  break     def   delstatic   cls attr              Static variable deleter            for c in cls   sro                if attr in StaticVarsMeta statics c                   try                      delattr c attr                      break                 except AttributeError                      pass         raise AttributeError cls   name       object has no attribute   0    format attr       def   delattr   cls attr              Prevent   sro   attribute from deletion            if attr       sro                 raise AttributeError  readonly attribute           super     delattr   attr      def is static cls attr              Returns True if an attribute is a static variable of any class in the   sro              if any attr in StaticVarsMeta statics c  for c in cls   sro                 return True         return False

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Variables declared inside the class definition  but not inside a method are class or static variables    gt  gt  gt  class MyClass          i   3      gt  gt  gt  MyClass i 3    As  millerdev points out  this creates a class-level i variable  but this is distinct from any instance-level i variable  so you could have   gt  gt  gt  m   MyClass    gt  gt  gt  m i   4  gt  gt  gt  MyClass i  m i  gt  gt  gt   3  4    This is different from C   and Java  but not so different from C   where a static member can t be accessed using a reference to an instance   See what the Python tutorial has to say on the subject of classes and class objects    Steve Johnson has already answered regarding static methods  also documented under  Built-in Functions  in the Python Library Reference   class C       staticmethod     def f arg1  arg2               beidy recommends classmethods over staticmethod  as the method then receives the class type as the first argument  but I m still a little fuzzy on the advantages of this approach over staticmethod  If you are too  then it probably doesn t matter

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It is possible to have static class variables  but probably not worth the effort   Here s a proof-of-concept written in Python 3 -- if any of the exact details are wrong the code can be tweaked to match just about whatever you mean by a static variable     class Static      def   init   self  value  doc None           self deleted   False         self value   value         self   doc     doc     def   get   self  inst  cls None           if self deleted              raise AttributeError  Attribute not set           return self value     def   set   self  inst  value           self deleted   False         self value   value     def   delete   self  inst           self deleted   True  class StaticType type       def   delattr   cls  name           obj   cls   dict   get name          if isinstance obj  Static               obj   delete   name          else              super StaticType  cls    delattr   name      def   getattribute   cls   args           obj   super StaticType  cls    getattribute    args          if isinstance obj  Static               obj   obj   get   cls  cls   class            return obj     def   setattr   cls  name  val             check if object already exists         obj   cls   dict   get name          if isinstance obj  Static               obj   set   name  val          else              super StaticType  cls    setattr   name  val    and in use   class MyStatic metaclass StaticType               Testing static vars             a   Static 9      b   Static 12      c   3  class YourStatic MyStatic       d   Static  woo hoo       e   Static  doo wop     and some tests   ms1   MyStatic   ms2   MyStatic   ms3   MyStatic   assert ms1 a    ms2 a    ms3 a    MyStatic a assert ms1 b    ms2 b    ms3 b    MyStatic b assert ms1 c    ms2 c    ms3 c    MyStatic c ms1 a   77 assert ms1 a    ms2 a    ms3 a    MyStatic a ms2 b   99 assert ms1 b    ms2 b    ms3 b    MyStatic b MyStatic a   101 assert ms1 a    ms2 a    ms3 a    MyStatic a MyStatic b   139 assert ms1 b    ms2 b    ms3 b    MyStatic b del MyStatic b for inst in  ms1  ms2  ms3       try          getattr inst   b       except AttributeError          pass     else          print  AttributeError not raised on  r    attr  ms1 c   13 ms2 c   17 ms3 c   19 assert ms1 c    13 assert ms2 c    17 assert ms3 c    19 MyStatic c   43 assert ms1 c    13 assert ms2 c    17 assert ms3 c    19  ys1   YourStatic   ys2   YourStatic   ys3   YourStatic   MyStatic b    burgler  assert ys1 a    ys2 a    ys3 a    YourStatic a    MyStatic a assert ys1 b    ys2 b    ys3 b    YourStatic b    MyStatic b assert ys1 d    ys2 d    ys3 d    YourStatic d assert ys1 e    ys2 e    ys3 e    YourStatic e ys1 a    blah  assert ys1 a    ys2 a    ys3 a    YourStatic a    MyStatic a ys2 b    kelp  assert ys1 b    ys2 b    ys3 b    YourStatic b    MyStatic b ys1 d    fee  assert ys1 d    ys2 d    ys3 d    YourStatic d ys2 e    fie  assert ys1 e    ys2 e    ys3 e    YourStatic e MyStatic a    aargh  assert ys1 a    ys2 a    ys3 a    YourStatic a    MyStatic a

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You can use a list or a dictionary to get  static behavior  between instances   class Fud        class vars     origin open  False        def   init   self  origin   True            self origin   origin          self opened   True          if origin               self class vars  origin open     True        def make another fud self                Generating another Fud   from the origin instance               return Fud False         def close self            self opened   False          if self origin               self class vars  origin open     False   fud1   Fud   fud2   fud1 make another fud    print  f is this the original fud   fud2 origin    print  f is the original fud open   fud2 class vars  origin open        is this the original fud  False   is the original fud open  True  fud1 close    print  f is the original fud open   fud2 class vars  origin open        is the original fud open  False

User · Answer

You can also add class variables to classes on the fly   gt  gt  gt  class X          pass       gt  gt  gt  X bar   0  gt  gt  gt  x   X    gt  gt  gt  x bar 0  gt  gt  gt  x foo Traceback  most recent call last     File   lt interactive input gt    line 1  in  lt module gt  AttributeError  X instance has no attribute  foo   gt  gt  gt  X foo   1  gt  gt  gt  x foo 1   And class instances can change class variables  class X    l        def   init   self       self l append 1   print X   l print X   l   gt python test py  1   1  1

[python] Are static class variables possible in Python?

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