Python, import, module

When the interpreter reads a python script file, it does two things:

(1) set some special variable.

(2) it executes all the code from 1st line of that script file.

__name__ (2 underscores before and after) is a special python variable.

we can import this script as a module.

and also execute this script directly that the interpreter will assign the hard-coded string "__main__" to the __name__ variable

# foo.py
# I am using python 3.4

print ("Befor foo function.")
def foo():
    print ("foo function.")
print ("After foo function.")
if __name__ == "__main__":
    foo()

if we run it with

$ python foo.py

then the result is :

Befor foo function.

After foo function.

foo function.

and if we import it, then run $ python hello.py

# hello.py
import foo

the running result is:

Befor foo function.

After foo function.