Python Importlib loader.exec_module to run a function of a py file

Question

I have several .py files in several folders. I do os.walk and get all names of .py files in list files and prior to that I know that each .py contains a function test() which takes an integer and returns an integer (which is somewhat unique). I am using the following code. Where r is an integer, files contain the path of a py file, for example:

C://users//codebase//user1//int_user_1.py

for fil in files:
    spec = importlib.util.spec_from_file_location("test", fil)
    foo = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(foo)
    get_test = foo.test(r)

But the problem here is the line spec.loader.exec_module(foo) is executing all the code in the file fil from line 1 of that particular .py file, but not just the function fil.test(). How can I execute only fil.test() function?

EDIT-1: I am unable to make any changes to the content of fil.py.

Masklinn · Accepted Answer · 2020-02-11 07:04:57Z

1

How can I execute only fil.test() function?

Wrap all the non-declaration code in an if __name__ == '__main__' condition.

Python modules are executable code, loading a module means executing the body of the module in a special "module namespace". If there's code you don't want executed on import, you have to "gate" it, using the condition above: a module's __name__ is only "__main__" if the module is being directly executed e.g.

$ echo "print(__name__)" > foo.py
$ python foo.py
__main__
$ python -c 'import foo'
foo

answered Feb 11, 2020 at 7:04

Masklinn

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5 Comments

Ram Over a year ago

Do you mean wrap all the non-declaration code in fil.py in if name == 'main' condition? Unfortunately I cannot do that as I don't have edit access to those files.

Masklinn Over a year ago

"Do you mean wrap all the non-declaration code in fil.py in if name == 'main' condition?" yes "Unfortunately I cannot do that as I don't have edit access to those files." well then you're hosed.

Ram Over a year ago

Nope, I managed this particular thing in the past, but unfortunately I forgot how I did that.

Masklinn Over a year ago

Only way I can see to do that would be to parse the file (without executing it), extract the function declaration you're interested in and eval that somehow, probably alongside all the imports declared in the file, and possibly a bunch of constants. So no, I don't think you're anything but hosed.

Darryl Over a year ago

The line "def test():" is actually an assignment under the hood, kinda equivalent to the pseudocode "this_module.test = <function>". That assignment gets made by executing that line of code and the function body lines that follow. What you are actually asking for is a way to execute those lines of code without executing the file's other lines of code.

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