45

I want to call some unknown function with adding parameters using getattr function. Is it possible?

Ondrej Slinták
  • 31,386
  • 20
  • 94
  • 126
megido
  • 4,135
  • 6
  • 29
  • 33

3 Answers3

91

Yes, but you don't pass them to getattr(); you call the function as normal once you have a reference to it.

getattr(obj, 'func')('foo', 'bar', 42)
Ignacio Vazquez-Abrams
  • 776,304
  • 153
  • 1,341
  • 1,358
61

If you wish to invoke a dynamic method with a dynamic list of arguments / keyword arguments, you can do the following:

function_name = 'wibble'
args = ['flip', 'do']
kwargs = {'foo':'bar'}

getattr(obj, function_name)(*args, **kwargs)
Steve Mayne
  • 22,285
  • 4
  • 49
  • 49
-2

function to call

import sys

def wibble(a, b, foo='foo'):
    print(a, b, foo)
    
def wibble_without_kwargs(a, b):
    print(a, b)
    
def wibble_without_args(foo='foo'):
    print(foo)
    
def wibble_without_any_args():
    print('huhu')


# have to be in the same scope as wibble
def call_function_by_name(function_name, args=None, kwargs=None):
    if args is None:
        args = list()
    if kwargs is None:
        kwargs = dict()
    getattr(sys.modules[__name__], function_name)(*args, **kwargs)

    
call_function_by_name('wibble', args=['arg1', 'arg2'], kwargs={'foo': 'bar'})
call_function_by_name('wibble_without_kwargs', args=['arg1', 'arg2'])
call_function_by_name('wibble_without_args', kwargs={'foo': 'bar'})
call_function_by_name('wibble_without_any_args')
# output:
# arg1 arg2 bar
# arg1 arg2
# bar
# huhu
mGran
  • 1
  • 2
  • 1
    Don't set empty lists or dicts in the function declaration since they are evaluated immediately. – Sunny Patel Aug 10 '21 at 02:50
  • @SunnyPatel: Don't agree. With the empty list and dict declaration, the call_function_by_name is more universal. You can call functions without kwargs, args or even without any arguments. I modified my answer to make this clear. – mGran Aug 13 '21 at 06:23
  • @mGran, Sunny is pointing out that doing this is specifically an anti-pattern. There are many discussions on why setting an instance of an empty list/dict/etc in a function declaration doesn't do what many people think it will do, and why it will bite you. I'd suggest taking a look at some of those discussions. e.g. https://stackoverflow.com/questions/26320899/why-is-the-empty-dictionary-a-dangerous-default-value-in-python or https://stackoverflow.com/questions/1132941/least-astonishment-and-the-mutable-default-argument to make sure you understand the implications of doing this. – Zeb Oct 20 '21 at 17:43
  • 1
    @Zeb You have got a point. I edited the answer. – mGran Oct 23 '21 at 06:41