Static methods in Python

Question

Is it possible to have static methods in Python which I could call without initializing a class  like   ClassName static method

User · Answer

I encounter this question from time to time. The use case and example that I am fond of is:

jeffs@jeffs-desktop:/home/jeffs  $ python36
Python 3.6.1 (default, Sep  7 2017, 16:36:03) 
[GCC 6.3.0 20170406] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cmath
>>> print(cmath.sqrt(-4))
2j
>>>
>>> dir(cmath)
['__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atanh', 'cos', 'cosh', 'e', 'exp', 'inf', 'infj', 'isclose', 'isfinite', 'isinf', 'isnan', 'log', 'log10', 'nan', 'nanj', 'phase', 'pi', 'polar', 'rect', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau']
>>>

It does not make sense to create an object of class cmath, because there is no state in a cmath object. However, cmath is a collection of methods that are all related in some way. In my example above, all of the functions in cmath act on complex numbers in some way.

User · Answer

I think that Steven is actually right  To answer the original question  then  in order to set up a class method  simply assume that the first argument is not going to be a calling instance  and then make sure that you only call the method from the class    Note that this answer refers to Python 3 x  In Python 2 x you ll get a TypeError for calling the method on the class itself    For example   class Dog      count   0   this is a class variable     dogs        this is a class variable      def   init   self  name           self name   name  self name is an instance variable         Dog count    1         Dog dogs append name       def bark self  n     this is an instance method         print     says      format self name   woof      n        def rollCall n    this is implicitly a class method  see comments below          print  There are    dogs   format Dog count           if n  gt   len Dog dogs  or n  lt  0              print  They are                for dog in Dog dogs                  print        format dog           else              print  The dog indexed at    is      format n  Dog dogs n     fido   Dog  Fido   fido bark 3  Dog rollCall -1  rex   Dog  Rex   Dog rollCall 0    In this code  the  rollCall  method assumes that the first argument is not an instance  as it would be if it were called by an instance instead of a class   As long as  rollCall  is called from the class rather than an instance  the code will work fine  If we try to call  rollCall  from an instance  e g    rex rollCall -1    however  it would cause an exception to be raised because it would send two arguments  itself and -1  and  rollCall  is only defined to accept one argument   Incidentally  rex rollCall   would send the correct number of arguments  but would also cause an exception to be raised because now n would be representing a Dog instance  i e   rex  when the function expects n to be numerical   This is where the decoration comes in  If we precede the  rollCall  method with   staticmethod   then  by explicitly stating that the method is static  we can even call it from an instance  Now    rex rollCall -1    would work  The insertion of  staticmethod before a method definition  then  stops an instance from sending itself as an argument   You can verify this by trying the following code with and without the  staticmethod line commented out   class Dog      count   0   this is a class variable     dogs        this is a class variable      def   init   self  name           self name   name  self name is an instance variable         Dog count    1         Dog dogs append name       def bark self  n     this is an instance method         print     says      format self name   woof      n         staticmethod     def rollCall n           print  There are    dogs   format Dog count           if n  gt   len Dog dogs  or n  lt  0              print  They are                for dog in Dog dogs                  print        format dog           else              print  The dog indexed at    is      format n  Dog dogs n      fido   Dog  Fido   fido bark 3  Dog rollCall -1  rex   Dog  Rex   Dog rollCall 0  rex rollCall -1

User · Answer

Yep  using the staticmethod decorator class MyClass object        staticmethod     def the static method x           print x   MyClass the static method 2     outputs 2  Note that some code might use the old method of defining a static method  using staticmethod as a function rather than a decorator  This should only be used if you have to support ancient versions of Python  2 2 and 2 3  class MyClass object       def the static method x           print x      the static method   staticmethod the static method   MyClass the static method 2     outputs 2  This is entirely identical to the first example  using  staticmethod   just not using the nice decorator syntax Finally  use staticmethod sparingly  There are very few situations where static-methods are necessary in Python  and I ve seen them used many times where a separate  quot top-level quot  function would have been clearer   The following is verbatim from the documentation    A static method does not receive an implicit first argument  To declare a static method  use this idiom  class C       staticmethod     def f arg1  arg2             The  staticmethod form is a function decorator     see the description of function definitions in Function definitions for details  It can be called either on the class  such as C f    or on an instance  such as C   f     The instance is ignored except for its class  Static methods in Python are similar to those found in Java or C    For a more advanced concept  see classmethod    For more information on static methods  consult the documentation on the standard type hierarchy in The standard type hierarchy  New in version 2 2  Changed in version 2 4  Function decorator syntax added

User · Answer

Static methods in Python       Is it possible to have static methods in Python so I can call them   without initializing a class  like   ClassName StaticMethod      Yes  static methods can be created like this  although it s a bit more Pythonic to use underscores instead of CamelCase for methods    class ClassName object         staticmethod     def static method kwarg1 None              return a value that is a function of kwarg1      The above uses the decorator syntax  This syntax is equivalent to   class ClassName object        def static method kwarg1 None              return a value that is a function of kwarg1         static method   staticmethod static method    This can be used just as you described   ClassName static method     A builtin example of a static method is str maketrans   in Python 3  which was a function in the string module in Python 2     Another option that can be used as you describe is the classmethod  the difference is that the classmethod gets the class as an implicit first argument  and if subclassed  then it gets the subclass as the implicit first argument   class ClassName object         classmethod     def class method cls  kwarg1 None              return a value that is a function of the class and kwarg1      Note that cls is not a required name for the first argument  but most experienced Python coders will consider it badly done if you use anything else   These are typically used as alternative constructors    new instance   ClassName class method     A builtin example is dict fromkeys     new dict   dict fromkeys   key1    key2

User · Answer

So  static methods are the methods which can be called without creating the object of a class  For Example  -       staticmethod     def add a  b           return a   b  b   A add 12 12  print b   In the above example method add is called by the class name A not the object name

User · Answer

Yes  check out the staticmethod decorator    gt  gt  gt  class C           staticmethod         def hello                    print  Hello World       gt  gt  gt  C hello   Hello World

User · Answer

Python Static methods can be created in two ways     Using staticmethod    class Arithmetic      def add x  y           return x   y   create add static method Arithmetic add   staticmethod Arithmetic add   print  Result    Arithmetic add 15  10      Output   Result  25   Using  staticmethod  class Arithmetic     create add static method  staticmethod def add x  y       return x   y  print  Result    Arithmetic add 15  10      Output   Result  25

User · Answer

You don t really need to use the  staticmethod decorator  Just declaring a method  that doesn t expect the self parameter  and call it from the class  The decorator is only there in case you want to be able to call it from an instance as well  which was not what you wanted to do   Mostly  you just use functions though

User · Answer

Perhaps the simplest option is just to put those functions outside of the class   class Dog object       def   init   self  name           self name   name      def bark self           if self name     Doggy               return barking sound           else              return  yip yip   def barking sound        return  woof woof    Using this method  functions which modify or use internal object state  have side effects  can be kept in the class  and the reusable utility functions can be moved outside   Let s say this file is called dogs py  To use these  you d call dogs barking sound   instead of dogs Dog barking sound   If you really need a static method to be part of the class  you can use the staticmethod decorator

User · Answer

Aside from the particularities of how static method objects behave  there is a certain kind of beauty you can strike with them when it comes to organizing your module-level code     garden py def trim a       pass  def strip a       pass  def bunch a  b       pass  def  foo foo       pass  class powertools object               Provides much regarded gardening power tools               staticmethod     def answer to the ultimate question of life the universe and everything            return 42       staticmethod     def random            return 13       staticmethod     def promise            return True  def  bar baz  quux       pass  class  Dice object       pass  class  6d  Dice       pass  class  12d  Dice       pass  class  Smarter      pass  class  MagicalPonies      pass  class  Samurai      pass  class Foo  6d   Samurai       pass  class Bar  12d   Smarter   MagicalPonies       pass          tests py import unittest import garden  class GardenTests unittest TestCase       pass  class PowertoolsTests unittest TestCase       pass  class FooTests unittest TestCase       pass  class BarTests unittest TestCase       pass          interactive py from garden import trim  bunch  Foo  f   trim Foo    bunch f  Foo             my garden py import garden from garden import powertools  class  Cowboy garden  Samurai       def hit            return powertools promise   and powertools random   or 0  class Foo  Cowboy  garden Foo       pass   It now becomes a bit more intuitive and self-documenting in which context certain components are meant to be used and it pans out ideally for naming distinct test cases as well as having a straightforward approach to how test modules map to actual modules under tests for purists   I frequently find it viable to apply this approach to organizing a project s utility code  Quite often  people immediately rush and create a utils package and end up with 9 modules of which one has 120 LOC and the rest are two dozen LOC at best  I prefer to start with this and convert it to a package and create modules only for the beasts that truly deserve them     utils py class socket object        staticmethod     def check if port available port           pass       staticmethod     def get free port port          pass  class image object        staticmethod     def to rgb image           pass       staticmethod     def to cmyk image           pass

[python] Static methods in Python?

Examples related to python

Examples related to static-methods