.py files are the original text files holing python code.
.pyc files are compiled versions of the .py files.
Whenever your code imports a module the interpreter imports the .pyc version of it if it's available and it has a later modification date than the .py file. If a .pyc file does not exist the interpreter compiles the .py file and saves it as .pyc.
A .pyc is not created for your main program file that you execute (only for imported modules).
The .pyc file contains encoded python bytecode.
