Call a Python method by name

If I have an object and a method name in a string, how can I call the method?

class Foo:
    def bar1(self):
        print 1
    def bar2(self):
        print 2

def callMethod(o, name):
    ???

f = Foo()
callMethod(f, "bar1")

Answers:

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Method 1

Use the built-in getattr() function:

class Foo:
    def bar1(self):
        print(1)
    def bar2(self):
        print(2)

def call_method(o, name):
    return getattr(o, name)()


f = Foo()
call_method(f, "bar1")  # prints 1

You can also use setattr() for setting class attributes by names.

Method 2

I had similar question, wanted to call instance method by reference. Here are funny things I found:

instance_of_foo=Foo()

method_ref=getattr(Foo, 'bar')
method_ref(instance_of_foo) # instance_of_foo becomes self

instance_method_ref=getattr(instance_of_foo, 'bar')
instance_method_ref() # instance_of_foo already bound into reference

Python is amazing!

Method 3

getattr(globals()['Foo'](), 'bar1')()
getattr(globals()['Foo'](), 'bar2')()

No need to instantiate Foo first!

Method 4

def callmethod(cls, mtd_name):    
    method = getattr(cls, mtd_name)
    method()

Method 5

Here is a more generalized version using Python decorators. You can call by short or long name. I found it useful when implementing CLI with short and long sub commands.

Python decorators are wonderful. Bruce Eckel (Thinking in Java) describes Python decorators beautifully here.

http://www.artima.com/weblogs/viewpost.jsp?thread=240808
http://www.artima.com/weblogs/viewpost.jsp?thread=240845

#!/usr/bin/env python2

from functools import wraps


class CommandInfo(object):
    cmds = []

    def __init__(self, shortname, longname, func):
        self.shortname = shortname
        self.longname = longname
        self.func = func


class CommandDispatch(object):
    def __init__(self, shortname, longname):
        self.shortname = shortname
        self.longname = longname

    def __call__(self, func):
        print("hello from CommandDispatch's __call__")

        @wraps(func)
        def wrapped_func(wself, *args, **kwargs):
            print('hello from wrapped_func, args:{0}, kwargs: {1}'.format(args, kwargs))
            func(wself, *args, **kwargs)

        ci = CommandInfo
        ci.cmds += [ci(shortname=self.shortname, longname=self.longname, func=func)]
        return wrapped_func

    @staticmethod
    def func(name):
        print('hello from CommandDispatch.func')

        for ci in CommandInfo.cmds:
            if ci.shortname == name or ci.longname == name:
                return ci.func

        raise RuntimeError('unknown command')


@CommandDispatch(shortname='co', longname='commit')
def commit(msg):
    print('commit msg: {}'.format(msg))


commit('sample commit msg')         # Normal call by function name

cd = CommandDispatch
short_f = cd.func(name='co')        # Call by shortname
short_f('short sample commit msg')

long_f = cd.func(name='commit')     # Call by longname
long_f('long sample commit msg')


class A(object):
    @CommandDispatch(shortname='Aa', longname='classAmethoda')
    def a(self, msg):
        print('A.a called, msg: {}'.format(msg))


a = A()
short_fA = cd.func(name='Aa')
short_fA(a, 'short A.a msg')

long_fA = cd.func(name='classAmethoda')
long_fA(a, 'short A.a msg')

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