Calling a function of a module by using its name a string

Question

What is the best way to go about calling a function given a string with the function s name in a Python program   For example  let s say that I have a module foo  and I have a string whose content is  bar   What is the best way to call foo bar     I need to get the return value of the function  which is why I don t just use eval  I figured out how to do it by using eval to define a temp function that returns the result of that function call  but I m hoping that there is a more elegant way to do this

User · Answer

Try this  While this still uses eval  it only uses it to summon the function from the current context  Then  you have the real function to use as you wish   The main benefit for me from this is that you will get any eval-related errors at the point of summoning the function  Then you will get only the function-related errors when you call   def say hello name       print  Hello      format name     get the function by name method name    say hello  method   eval method name     call it like a regular function later args     friend   kwargs      method  args    kwargs

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For what it s worth  if you needed to pass the function  or class  name and app name as a string  then you could do this   myFnName     MyFn  myAppName    MyApp  app   sys modules myAppName  fn    getattr app myFnName

User · Answer

locals    myfunction       or  globals    myfunction       locals returns a dictionary with a current local symbol table  globals returns a dictionary with global symbol table

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The answer  I hope  no one ever wanted  Eval like behavior  getattr locals   get  foo   or globals   get  foo     bar       Why not add auto-importing  getattr      locals   get  foo   or      globals   get  foo   or       import    foo      bar       In case we have extra dictionaries we want to check  getattr next  x for x in  f  foo   for f in                             locals   get  globals   get                              self   dict   get    import                    if x     bar       We need to go deeper  getattr next  x for x in  f  foo   for f in                  locals   get  globals   get  self   dict   get                    d get for d in  list dd values    for dd in                                   locals   globals   self   dict                                    if isinstance dd dict                   if isinstance d dict                        import               if x     bar

User · Answer

none of what was suggested helped me  I did discover this though    lt object gt    getattribute    lt string name gt    lt params gt     I am using python 2 66   Hope this helps

User · Answer

Given a string  with a complete python path to a function  this is how I went about getting the result of said function   import importlib function string    mypackage mymodule myfunc  mod name  func name   function string rsplit     1  mod   importlib import module mod name  func   getattr mod  func name  result   func

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Patrick s solution is probably the cleanest  If you need to dynamically pick up the module as well  you can import it like   module     import    foo   func   getattr module   bar   func

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Assuming module foo with method bar   import foo method to call   getattr foo   bar   result   method to call     You could shorten lines 2 and 3 to   result   getattr foo   bar       if that makes more sense for your use case    You can use getattr in this fashion on class instance bound methods  module-level methods  class methods    the list goes on

User · Answer

Just a simple contribution  If the class that we need to instance is in the same file  we can use something like this     Get class from globals and create an instance m   globals    our class        Get the function  from the instance  that we need to call func   getattr m   function name      Call it func     For example   class A      def   init   self           pass      def sampleFunc self  arg           print  you called sampleFunc      format arg    m   globals    A     func   getattr m   sampleFunc   func  sample arg      Sample  all on one line getattr globals    A       sampleFunc    sample arg     And  if not a class   def sampleFunc arg       print  you called sampleFunc      format arg    globals    sampleFunc    sample arg

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As this question How to dynamically call methods within a class using method-name assignment to a variable  duplicate  marked as a duplicate as this one  I am posting a related answer here   The scenario is  a method in a class want to call another method on the same class dynamically  I have added some details to original example which offers some wider scenario and clarity   class MyClass      def   init   self  i           self i   i      def get self           func   getattr MyClass   function    format self i           func self  12      This one will work           self func 12       But this does NOT work        def function1 self  p1           print  function1      format p1             do other stuff      def function2 self  p1           print  function2      format p1             do other stuff   if   name         main         class1   MyClass 1      class1 get       class2   MyClass 2      class2 get        Output  Python 3 7 x       function1  12       function2  12

User · Answer

Although getattr   is elegant  and about 7x faster  method  you can get return value from the function  local  class method  module  with eval as elegant as x   eval  foo bar      And when you implement some error handling then quite securely  the same principle can be used for getattr   Example with module import and class    import module  call module function  pass parameters and print retured value with eval    import random bar    random randint  randint   eval bar  0 100  print randint    will print random int from  lt 0 100     also class method returning  or not  value s  can be used with eval   class Say      def say something  nothing            return something  bar    Say say  print eval bar   nice to meet you too      will print  nice to meet you    When module or class does not exist  typo or anything better  then NameError is raised  When function does not exist  then AttributeError is raised  This can be used to handle errors    try except block can be used to catch both errors try      eval  Say talk       raises AttributeError because function does not exist     eval  Says say       raises NameError because the class does not exist       or the same with getattr      getattr Say   talk       raises AttributeError     getattr Says   say       raises NameError except AttributeError        do domething or just        print  Function does not exist   except NameError        do domething or just        print  Module does not exist

User · Answer

This is a simple answer  this will allow you to clear the screen for example  There are two examples below  with eval and exec  that will print 0 at the top after cleaning  if you re using Windows  change clear to cls  Linux and Mac users leave as is for example  or just execute it  respectively   eval  os system   clear      exec  os system   clear

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getattr calls method by name from an object  But this object should be parent of calling class  The parent class can be got by super self   class    self  class Base      def call base func            quot  quot  quot This does not work quot  quot  quot          def new func self   args    kwargs               name   func   name               getattr super self   class    self   name   args    kwargs          return new func      def f self   args           print f quot BASE method invoked  quot        def g self   args           print f quot BASE method invoked  quot    class Inherit Base        Base call base     def f self   args            quot  quot  quot function body will be ignored by the decorator  quot  quot  quot          pass       Base call base     def g self   args            quot  quot  quot function body will be ignored by the decorator  quot  quot  quot          pass  Inherit   f     The goal is to print  quot BASE method invoked  quot

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The best answer according to the Python programming FAQ would be   functions     myfoo   foo bar   mystring    myfoo  if mystring in functions      functions mystring         The primary advantage of this technique is that the strings do not need to match the names of the functions  This is also the primary technique used to emulate a case construct

[python] Calling a function of a module by using its name (a string)

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