How to check for a function type in Python?

Question

I've got a list of things, of which some can also be functions. If it is a function I would like to execute it. For this I do a type-check. This normally works for other types, like str, int or float. But for a function it doesn't seem to work:

>>> def f():
...     pass
... 
>>> type(f)
<type 'function'>
>>> if type(f) == function: print 'It is a function!!'
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'function' is not defined
>>>

Does anybody know how I can check for a function type?

You can also use try/except instead of checking for type.

Paulo Almeida
– Paulo Almeida

2013-07-12 11:02:08 +00:00
Commented Jul 12, 2013 at 11:02 — Paulo Almeida
– Paulo Almeida, Commented Jul 12, 2013 at 11:02

Daniel Roseman · Accepted Answer · 2013-07-12 10:21:51Z

21

Don't check types, check actions. You don't actually care if it's a function (it might be a class instance with a __call__ method, for example) - you just care if it can be called. So use callable(f).

answered Jul 12, 2013 at 10:21

Daniel Roseman

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Comments

TerryA · Accepted Answer · 2013-07-12 10:38:14Z

5

Because function isn't a built-in type, a NameError is raised. If you want to check whether something is a function, use hasattr:

>>> hasattr(f, '__call__')
True

Or you can use isinstance():

>>> from collections import Callable
>>> isinstance(f, Callable)
True
>>> isinstance(map, Callable)
True

edited Jul 12, 2013 at 10:38

answered Jul 12, 2013 at 10:21

TerryA

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7 Comments

zhangyangyu Over a year ago

isinstance is not good for isinstance(map, types.FunctionType) returns False. Builtin functions are different not to mention the callable class.

TerryA Over a year ago

@zhangyangyu For built-in functions, you can use inspect.isbuiltin

stalk Over a year ago

There is collections.Callable. It works for buitlin functions too: isinstance(map, collections.Callable) returns True

kramer65 Over a year ago

@stalk - What's the difference between collections.Callable and simply callable (as suggested by DanielRoseman)?

stalk Over a year ago

@kramer65 well, i think it just another solution. callable() looks like more simplier.

|

Maerlyn · Accepted Answer · 2013-09-11 11:48:56Z

4

import types

if type(f) == types.FunctionType: 
    print 'It is a function!!'

edited Sep 11, 2013 at 11:48

Maerlyn

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answered Sep 11, 2013 at 9:12

user1251416

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1 Comment

phpjunkie Over a year ago

I was trying to get the magic methods, the dunders, to pop up in PyCharm after typing a period and this one worked.

stalk · Accepted Answer · 2013-07-12 10:37:12Z

3

collections.Callable can be used:

import collections

print isinstance(f, collections.Callable)

answered Jul 12, 2013 at 10:37

stalk

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1 Comment

user395760 Over a year ago

And in new-ish Python 3 versions (I think it's 3.2+) callable is re-introduced as a shorthand for this.

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