In chapters two through nine of this book, we looked at a number of techniques for designing classes, which are the foundation of object-oriented design and programming. The module is a collection of classes; it is a higher-level grouping of related classes and functions. It's rare to try to reuse a single class in isolation.
Consequently, the module is a fundamental component of Python implementation and reuse. A properly designed module can be reused because the needed classes and functions are bundled together. All Python programming is provided at the module level.
A Python module is a file. The filename extension must be .py. The filename in front of .py must be a valid Python name. Section 2.3 of Python Language Reference provides us with the complete definition of a name. One of the clauses in this definition is as follows:
