with - python execute string command line




Calling a function of a module by using its name(a string) (8)

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

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.


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.


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()

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')

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")()

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


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)

none of what was suggested helped me. I did discover this though.

<object>.__getattribute__(<string name>)(<params>)

I am using python 2.66

Hope this helps





object