"Write a Python program that encrypts and decrypts using an affine cipher. Input should be a plaintext message and an affine key (a,b). Output should be a cipher text for encrypting and plaintext for decrypting. You will need functions to eliminate spacing, capitalization, and punctuation and to convert characters to numerical values"

Note: plain text will only use the alphabet a-z.

This is a homework assignment for my math class where I am not being taught the actually programming. I have no book and I do not know anything about programming so I need the most basic/beginner and easily understood python program as I might have to present the assignment in class.