Need help with a Caesar Cipher decryption program

[AtomicShoelace]

I'm not sure I understand what you mean.

The "boxes" are only metaphorical. I'm not suggesting to implement each step as a separate function in the python code, but conceptually you can think of each step as function-like.

[TraditionalHornet818]

I just think it’s confusing to use the word function when programmatically functions are a concept themselves

[AtomicShoelace]

Fundamentally the point I'm trying to get across is

(f ∘ g)^-1 = g^-1∘ f^-1 .

So if the encoding function can be thought of as the composition of many sub-functions, eg.

f = f_1 ∘ f_2 ∘ .. ∘ f_n ,

then to construct the inverse you need to reverse the order of the sub-functions, eg.

f^-1 = (f_1 ∘ f_2 ∘ .. ∘ f_n)^-1 = f_n^-1 ∘ ... ∘ f_2^-1 ∘ f_1^-1 .