Python check if function exists without running it

Question

In python how do you check if a function exists without actually running the function (i.e. using try)? I would be testing if it exists in a module.

Laddy

Depend on the context, if is a class, if is global defined, you-ll have to extend the question to provide more elements. – Nutshell

Answer 1

You can use dir to check if a name is in a module:

>>> import os
>>> "walk" in dir(os)
True
>>>

In the sample code above, we test for the os.walk function.

Sokotra

And then to see if it's actually a function, callable(getattr(os,'walk')) – Kliment

What if I want to know if it exists at a global namespace (or from existing imports)? – Ephrayim

Use callable(getattr(os,'walk', None)) if you don't want to throw an exception – Antependium

Answer 2

You suggested try except. You could indeed use that:

try:
    variable
except NameError:
    print("Not in scope!")
else:
    print("In scope!")

This checks if variable is in scope (it doesn't call the function).

Diatomite

They specifically said without running the function and gave try as an example of what they don't want to do. – Statue

@Statue This doesn't call the function - that would require variable(). It just checks if variable is defined. – Diatomite

Oh I didn't realise you could do that. I don't seem to be able to remove the downvote unless you edit your answer. Can you change something minor so I can remove it? – Statue

Answer 3

Solution1:
import inspect
if (hasattr(m, 'f') and inspect.isfunction(m.f))

Solution2:
import inspect
if ('f' in dir(m) and inspect.isfunction(m.f))

where:
m = module name
f = function defined in m

Claudineclaudio

Answer 4

If you are checking if function exists in a package:

import pkg

print("method" in dir(pkg))

If you are checking if function exists in your script / namespace:

def hello():
    print("hello")

print("hello" in dir())

Houseyhousey

Answer 5

if you are looking for a function in your code, use global()

if "function" in globals():
  ...

Toxemia

Answer 6

If you are looking for the function in class, you can use a "__dict__" option. E.g to check if the function "some_function" in "some_class" do:

if "some_function" in list(some_class.__dict__.keys()):
    print('Function {} found'.format ("some_function"))

Thee

You should just use hasattr(some_class, "some_function") for more clarity and because sometimes dict is not used, although this still does not check whether you’re dealing with a function or not. – Bechuanaland

Answer 7

Just wanted to add my solution here. It's 8 years late, and similar variant been suggested, but here is more capable version. Just for those, who find this as i did.

def check(fn):
    def c():pass
    for item in globals().keys():
        if type(globals()[item]) == type(c) and fn == item:
            return print(item, "is Function!")
        elif fn == item:
            return print(fn, "is", type(globals()[item]))
    return print("Can't find", fn)

Rea

Answer 8

I believe this work also and look simpler for me:

def newFunc():
    print("hello")

if newFunc:
    print("newFunc function is exist")
else:
    print("newFunc function is not exist")

Asymptotic