How to Structure a Program
Generally, a Python program consists of multiple text files containing Python statements. The program is structured as one main, top-level file, along with zero or more supplemental files known as modules in Python.
In Python, the top-level (a.k.a. script) file contains the main flow of control of your program—this is the file you run to launch your application. The module files are libraries of tools used to collect components used by the top-level file (and possibly elsewhere). Top-level files use tools defined in module files, and modules use tools defined in other modules.
Module files generally don’t do anything when run directly; rather, they define tools intended for use in other files. In Python, a file imports a module to gain access to the tools it defines, which are known as its attributes (i.e., variable names attached to objects such as functions). Ultimately, we import modules and access their attributes to use their tools.
