Why does a line of code that is outside a function (when the function is called in another file) pri-CodePudding

When I create a function in a file (let's call it demostration_1.py) and some other line of code outside the function, as shown below:

def adult(x):
    return x >= 18

print('hello world')

and then I call this function in another file (let's call it demostration_2.py)

from demostration_1 import adult

print(adult(18))

it prints out

hello world
True

So, Why does it print hello world if I'm only calling for the adult() function?

CodePudding user response：

just to expand on my comment above, but imagine that your module a contains the following code:

def adult(x):
    return x >= MIN_YEARS


MIN_YEARS = 18

This works perfectly fine, but only because the entire module is loaded when you call import a or from a import adult.

But if you didn't want a block of code to be run whenever a module was imported, you can hide that logic away within an if __name__=='__main__:' block at the end of the file, as @Tim Roberts also mentioned. So with the below approach, you won't see hello world printed whenever this module is imported by another one.

def adult(x):
    return x >= 18


if __name__ == '__main__':
    print('hello world')