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Python import system: Using the -m command line option

The command line option -m runs a module as a script. If the module is a package (that is essentially a directory), it runs (or tries to run) __main__.py.

This is demonstrated with the following simple example: A directory, named minusM, contains three files:

__init__.py,
__main__.py and
mod.py

Their content is one print() statement only: __init__.py:

print('minusM: __init__.py')

Github repository about-Python, path: /import-system/minusM/__init__.py

__main__.py:

print('minusM: __main__.py')

Github repository about-Python, path: /import-system/minusM/__main__.py

__mod__.py:

print('minusM.mod')

Github repository about-Python, path: /import-system/minusM/mod.py

If the Python interpreter is started in the directory that contains minusM like so:

python -m minusM

the following is printed:

minusM: __init__.py
minusM: __main__.py

If the interpreter is started like so:

python -m minusM.mod

this is printed:

minusM: __init__.py
minusM.mod

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