2.2 General Python terminology

If you're reading this document, you probably have a good idea of what modules, extensions, and so forth are. Nevertheless, just to be sure that everyone is operating from a common starting point, we offer the following glossary of common Python terms:

the basic unit of code reusability in Python: a block of code imported by some other code. Three types of modules concern us here: pure Python modules, extension modules, and packages.
pure Python module
a module written in Python and contained in a single .py file (and possibly associated .pyc and/or .pyo files). Sometimes referred to as a ``pure module.''
extension module
a module written in the low-level language of the Python implemention: C/C++ for CPython, Java for JPython. Typically contained in a single dynamically loadable pre-compiled file, e.g. a shared object (.so) file for CPython extensions on Unix, a DLL (given the .pyd extension) for CPython extensions on Windows, or a Java class file for JPython extensions. (Note that currently, the Distutils only handles C/C++ extensions for CPython.)
a module that contains other modules; typically contained in a directory in the filesystem and distinguished from other directories by the presence of a file __init__.py.
root package
the root of the hierarchy of packages. (This isn't really a package, since it doesn't have an __init__.py file. But we have to call it something.) The vast majority of the standard library is in the root package, as are many small, standalone third-party modules that don't belong to a larger module collection. Unlike regular packages, modules in the root package can be found in many directories: in fact, every directory listed in sys.path can contribute modules to the root package.

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