if the content of foo.py
print __name__
if __name__ == '__main__':
print 'XXXX'
A file foo.py can be used in two ways.
- imported in another file :
import foo
In this case __name__ is foo, the code section does not get executed and does not print XXXX.
- executed directly :
python foo.py
When it is executed directly, __name__ is same as __main__ and the code in that section is executed and prints XXXX
One of the use of this functionality to write various kind of unit tests within the same module.