When importing a function it runs the whole script?

Question

I'm new to python and doing an assignment. It's meant to be done with linux but as I'm doing it by myself on my own computer I'm doing it on windows.

I've been trying to do this test system that we use looking like this:

>>> import file
>>> file.function(x)
"Answer that we want"

Then we run it through the linux terminal. I've been trying to create my own way of doing this by making a test file which imports the file and runs the function. But then on the other hand of just running the function it runs the whole script. Even though it's never been called to do that.

Import file
file.function(x)

That's pretty much what I've been doing but it runs the whole "file". I've also tried from file import function; it does the same.

What kind of script can I use to script the "answer that I want" for the testfile? As when we run in through linux terminal it says if it has failed or scored.

Answer 1

importing a file is equivalent to running it.

When you import a file (module), a new module object is created, and upon executing the module, every new identifier is put into the object as an attribute.

So if you don't want the module to do anything upon importing, rewrite it so it only has assignments and function definitions.

If you want it to run something only when invoked directly, you can do

A = whatever

def b():
    ...

if __name__ == '__main__'
    # write code to be executed only on direct execution, but not on import
    # This is because direct execution assigns `'__main__'` to `__name__` while import of any way assigns the name under which it is imported.

This holds no matter if you do import module or from module import function, as these do the same. Only the final assignment is different:

import module does:

• Check sys.modules, and if the module name isn't contained there, import it.
• Assign the identifier module to the module object.

from module import function does

• Check sys.modules, and if the module name isn't contained there, import it. (Same step as above).
• Assign the identifier function to the module object's attribute function.

Answer 2

You can check if the module is imported or executed with the __name__ attribute. If the script is executed the attribute is '__main__'.

It is also good style to define a main function that contains the code that should be executed.

def main()
    # do something
    pass

if __name__ == '__main__'
    main()