Python, checking if a module has a certain function

Question

I need to know if a python module function exists, without importing it.

Importing something that might not exist (not what I want): This is what I have so far, but it only works for whole modules not module functions.

import imp
try:
    imp.find_module('mymodule')
    found = True
except ImportError:
    found = False

The code above works for finding if the module exists, the code below is the functionality that I want, but this code doesn't work.

import imp
try:
    imp.find_module('mymodule.myfunction')
    found = True
except ImportError:
    found = False

It gives this error:

No module named mymodule.myfunction

I know that mymodule.myfunction does exist as a function because I can use it if I import it using:

import mymodule.myfunction

But, I am aware that it is not a module, so this error does make sense, I just don't know how to get around it.

Maybe you can try to import it then remove it from the sys.modules but I am not sure how it works. — clemtoy
– clemtoy, Commented Jul 31, 2015 at 20:44

cbuchart · Accepted Answer · 2017-05-05 08:43:45Z

6

Use hasattr function, which returns whether a function exists or not:

example 1)

hasattr(math,'tan')     --> true

example 2)

hasattr(math,'hhhhhh')  --> false

edited May 5, 2017 at 8:43

cbuchart

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answered May 5, 2017 at 8:25

Venkat Rajanala

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Comments

Ewan · Accepted Answer · 2015-07-31 20:29:34Z

5

What about:

try:
    from mymodule import myfunction
except ImportError:
    def myfunction():
        print("broken")

answered Jul 31, 2015 at 20:29

Ewan

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3 Comments

Malik Brahimi Over a year ago

I like this ask for forgiveness approach!

Rorschach Over a year ago

This isn't exactly what I was asking for, but I think will work for the functionality that i was going for. Thank you.

Ewan Over a year ago

@Rorschach - no worries. if I've helped you out please accept my answer. Thanks.

Patrick Maupin · Accepted Answer · 2015-07-31 20:33:04Z

1

I know that mymodule.myfunction does exist as a function because I can use it if I import it using:

import mymodule.myfunction

No -- if that works, then myfunction is a sub-module of the mymodule package.

You can import a module and inspect its vars(), or do a dir() on it, or even use a package like astor to inspect it without importing it. But your problem here would seem to be a lot more basic -- if you can type import mymodule.myfunction and not get an error, then myfunction is lying to you -- it's not really a function.

edited Jul 31, 2015 at 20:33

answered Jul 31, 2015 at 20:30

Patrick Maupin

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4 Comments

Rorschach Over a year ago

would you call it a submodule if it is defined like this: def myfunction: ... Or would you call it a function?

Patrick Maupin Over a year ago

That's a function. But you won't get that if you type import mymodule.myfunction. If you don't believe me, then after the import, print out information about myfunction after the import, e.g. print(mymodule.myfunction)

Rorschach Over a year ago

I believe you, I was just curious about which part I was wrong about.

Patrick Maupin Over a year ago

The part that I quoted. You said that "you know that ... exists as a function because you can import it with ..." That's a confusing misstatement, because Python just doesn't work that way. If you want to import a function from a module, you can use from ... import, like in your accepted answer, but you just cannot do what you claimed you did in your question.

o11c · Accepted Answer · 2019-03-01 22:27:13Z

-5

What you want is impossible.

You fundamentally cannot determine what is in a module without executing it.

Edit since I'm still getting downvotes: the other answers are answering a different question, not the one that was asked. Consider the following:

import random, string

globals()['generated_' + random.choice(string.ascii_lowercase)] = "what's my name?"

print(sorted(globals()))

There is no way to guess what variable(s) will be created without having the side-effects happen. And this kind of dynamic code is fairly common.

edited Mar 1, 2019 at 22:27

answered Jul 31, 2015 at 20:33

o11c

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7 Comments

Patrick Maupin Over a year ago

Absolutely not true. There are several packages that will let you inspect code without executing it.

o11c Over a year ago

@PatrickMaupin None of which can produce accurate results. Trust me, I'm working on one such package right now.

Patrick Maupin Over a year ago

@o11c -- sure, it's impossible, just like the halting problem. But, then it's impossible if you import the module, as well. Even ModuleType can be subclassed, and the __item__ method replaced with something... The point is, for most normal code that is imported by most normal people, either one works fine, but neither one will work in all cases.

o11c Over a year ago

@PatrickMaupin This is a lot of real-world code that messes with the globals as a dict, or does glob imports, or performs multiple/conditional assignments / deletions, or ...

Patrick Maupin Over a year ago

@o11c -- Absolutely. But you have to look at what the invoking real-world code might be interested in, as well. It typically won't be interested in every obscure deleted initialization function.

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