I get daily interview coding problems in the mail, this was the jerkiest way I could think of to do run length encoding

run_length_encoding.py

"""
Run-length encoding is a fast and simple method of encoding strings. 
The basic idea is to represent repeated successive characters 
as a single count and character. For example, the string 
"AAAABBBCCDAA" would be encoded as "4A3B2C1D2A".

Implement run-length encoding and decoding. You can assume 
the string to be encoded has no digits and consists solely of alphabetic 
characters. You can assume the string to be decoded is valid.
"""
import itertools
import re

def encode(s: str) -> str:
    return ''.join(str(len(list(group))) + c 
                   for c, group in itertools.groupby(s))

assert encode("AAAABBBCCDAA") == "4A3B2C1D2A"

REGEX = "([0-9]+)([A-Za-z]+)"

def decode(s: str) -> str:
    return ''.join(int(count) * char
                   for count, char in re.findall(REGEX, s))

assert decode("4A3B2C1D2A") == "AAAABBBCCDAA"