how to map letter to numbers in python code example

Example: turn characters to alpgabetic numper python

text = input()

def encrypt(t):
    chars = list(text)
    allowed_characters = list(" abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789,.?!")

    for char in chars:
        for i in allowed_characters:
            if char == i:
                chars[chars.index(char)] = allowed_characters.index(i)
    return chars

print(encrypt(text))