Python -m flag

python -m

The-m flag in Python is used to execute a module's content as the __main__ module directly from the command line. When the -m flag is followed by a module name, the Python interpreter will locate the module and execute its content. appdividend.com

The -m flag was added to Python 2.4.1 to provide an alternative means of identifying the Python module to execute from the command line. Initially, -m only worked with top-level module names, meaning modules that could be found directly on sys.path without any intervening package modules. However, with the completion of PEP 338, -m was extended to support module name representations beyond the top level, such as http.server. stackoverflow.com

The -m flag can be used to execute Python code from the command line via a module name, rather than a file name. It can also be used to add a directory to sys.path for use in import resolution, and to execute Python code that contains relative imports from the command line. stackoverflow.com

There are two notable use cases for the -m flag:

1. To execute modules from the command line for which one may not know their filename. This use case takes advantage of the fact that the Python interpreter knows how to convert module names to file names. This is particularly advantageous when one wants to run standard library modules or third-party modules from the command line. For example, one can execute the http.server module from the command line using python -m http.server. stackoverflow.com

2. To execute a local package containing absolute or relative imports without needing to install it. This use case is detailed in PEP 338 and leverages the fact that the current working directory is added to sys.path rather than the module's directory. This use case is very similar to using pip install -e . to install a package in develop/edit mode. stackoverflow.com

When executing a module via the -m flag, sys.path is modified to include the current directory, __name__ is set to '__main__', __package__ is set to the immediate parent package in the module name, and __init__.py is evaluated for all packages (including its own for package modules). __main__.py is evaluated for package modules, and the code is evaluated for code modules. stackoverflow.com

One major shortcoming of the -m flag is that it can only execute modules written in Python (i.e., *.py). If -m is used to execute a C compiled code module, the following error will be produced: "No code object available for ". stackoverflow.com