Three ways to run a python script file

Python offers three distinct ways to run a script or module, and each one affects sys.path, __name__, and import behavior in subtle but important ways.

Let’s break them down clearly:

The Three Ways to Run Python Code

1. Direct Script Execution

bash

python path/to/script.py

• ✅ Most common for quick scripts

• sys.path[0] is set to the directory containing the script

• __name__ == "__main__"

• ❌ Relative imports (like from .module import x) do not work

Example:

bash

cd project_root/package
python utils.py

Fails if utils.py uses relative imports.

2. Module Execution via -m

bash

python -m package.module

• ✅ Best for running code inside packages

• sys.path[0] is set to the directory containing the top-level package

• __name__ == "package.module"

• ✅ Relative imports work correctly

Example:

bash

cd project_root
python -m package.utils

Works perfectly with from .logger import formatter.

3. ‍ Interactive Mode / REPL / IPython

bash

python

Or:

bash

ipython

• ✅ Great for experimentation

• sys.path[0] is set to the current working directory (CWD)

• __name__ == "__main__" for any code typed or run

• ✅ Imports work if modules are in the CWD or PYTHONPATH

Example:

bash

cd project_root/package
python
>>> import utils  # works if utils.py is in CWD

Summary Table

Method	sys.path[0]	__name__	Relative Imports Work?
python script.py	Directory of script	"__main__"	❌ No
python -m package.mod	Directory of top-level pkg	"package.mod"	✅ Yes
Interactive / REPL	Current working directory	"__main__"	✅ Sometimes

Bonus: Making Your Script Flexible

You can make a module runnable both ways by adding:

python

if __name__ == "__main__":
    # CLI entry point or test logic

And using python -m package.module for proper relative imports.