If you want to call a function from another file in Python then there isn't any need to add file.py at the time of importing. You just need to write from file import function, and then call the function using function(a, b)and you are done. Now why not to use file.py is because it may not work, the file is one of Python's core modules, so it is better that you change the name of your file.
And an important note here that if you're trying to import some functions from file a.py to a file called b.py, make sure that a.py and b.py are in the same directory.
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