Conditional importing inside a function

[Roger]

I would like to have a file "functions.py" where I collect functions that might be usefull.
Different functions may require different imports. Instead of importing them all at the beginning I would like each function to only import if it has not already been imported.
I have tried -

#!/usr/bin/env python3
"""
Reuseable functions
"""

import sys

def filesize(url):
    """
    Reports size of file pointed to by url.
    """
    if "os" not in sys.modules:
        import os

    return os.path.getsize(url)

My IDE warns me that "os" after "return" is an unresolved reference.
Obviously the scope of the "import os" is limited to the if block.

Is there a way of making the "import os" global?

[Gribouillis]

The name os is a local variable in function filesize() because you have import os in the function's body. It doesn't matter whether the import is within an if block or not. On the other hand at runtime the import statement is not executed if 'os' is already in sys.modules and the local variable os is used prior to initialization and that's an error.

You can simply write

 
def filesize(url):
    """
    Reports size of file pointed to by url.
    """
    import os
    return os.path.getsize(url)

One of the first things the import statement does is checking if the module is already in sys.modules, so it is unecessary to do it yourself. Just import the module.