A module is a file containing Python definitions and statements. A module can define functions, classes, and variables, and it can include runnable code.

To create a module, you typically create a Python file with a “.py” extension.

__name__ is a special built-in variable that is used to differentiate whether a Python script is being run as the main program or if it is being imported as a module into another script.

The script will run when the module is the main program. If it is not the main program, then it will skip the if __name__ == "__main__": block.

sys.modules provides a dictionary that maps module names to the corresponding module objects. It is essentially a cache of all modules that have been imported.

To inspect the modules that have been imported during the current Python session.

sys.path returns the import paths where python will look in order to find files to import.

export PYTHONPATH = "file_path"

1. Python will first check the sys.modules cache to see if the module has already been imported. If so, it will use the reference in there.
2. Else, it will create a new module object and loads the source code from file and adds the entry to sys.modules

• Finder is responsible for finding the modules
• Loader is responsible to load the source code to compile and execute it.

A package is a collection of Python modules (and possibly other packages) organised in a directory.

A package is a way of organising related modules into a single directory hierarchy.

The __init__.py file tells python that the directory is a package as opposed to a standard directory.

We must import outer packages that the inner package is dependent on. If not, python will not be able to detect the sub packages.