14

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?

Improve this question
1
  • You can also use try/except instead of checking for type. Commented Jul 12, 2013 at 11:02

4 Answers 4

Reset to default
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).

Improve this answer
Sign up to request clarification or add additional context in comments.

Comments

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
Improve this answer

7 Comments

isinstance is not good for isinstance(map, types.FunctionType) returns False. Builtin functions are different not to mention the callable class.
@zhangyangyu For built-in functions, you can use inspect.isbuiltin
There is collections.Callable. It works for buitlin functions too: isinstance(map, collections.Callable) returns True
@stalk - What's the difference between collections.Callable and simply callable (as suggested by DanielRoseman)?
@kramer65 well, i think it just another solution. callable() looks like more simplier.
|
4 
import types

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

1 Comment

I was trying to get the magic methods, the dunders, to pop up in PyCharm after typing a period and this one worked.
3

collections.Callable can be used:

import collections

print isinstance(f, collections.Callable)
Improve this answer

1 Comment

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

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.