When you run a Python module with
python fibo.py <arguments>
the code in the module will be executed, just as if you imported it, but with the __name__ set to "__main__". That means that by adding this code at the end of your module:
if __name__ == "__main__":
import sys
fib(int(sys.argv[1]))
you can make the file usable as a script as well as an importable module, because the code that parses the command line only runs if the module is executed as the “main” file:
$ python fibo.py 50
1 1 2 3 5 8 13 21 34
If the module is imported, the code is not run:
>>> import fibo
>>>
This is often used either to provide a convenient user interface to a module, or for testing purposes (running the module as a script executes a test suite).
