Home Calling a function of a module by using its name (a string)
Reply: 9

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

ricree
1#
ricree Published in 2008-08-06 03:36:08Z

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 contents are "bar". What is the best way to go about calling 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.

Ben Hoyt
2#
Ben Hoyt Reply to 2017-02-22 18:10:17Z

Assuming module foo with method bar:

import foo
method_to_call = getattr(foo, 'bar')
result = method_to_call()

As far as that goes, lines 2 and 3 can be compressed 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.

Ben Hoyt
3#
Ben Hoyt Reply to 2017-02-22 18:08:23Z

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()
sastanin
4#
sastanin Reply to 2009-05-07 12:45:13Z
locals()["myfunction"]()

or

globals()["myfunction"]()

locals returns a dictionary with a current local symbol table. globals returns a dictionary with global symbol table.

trubliphone
5#
trubliphone Reply to 2012-02-14 05:55:36Z

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)
tbc0
6#
tbc0 Reply to 2014-09-22 21:49:18Z

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')
Natdrip
7#
Natdrip Reply to 2012-12-28 16:56:45Z

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

ferrouswheel
8#
ferrouswheel Reply to 2013-10-16 00:24:22Z

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()
00500005
9#
00500005 Reply to 2014-04-09 10:17:41Z

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")()
tvt173
10#
tvt173 Reply to 2016-10-24 13:20:46Z

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

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