Regex: How to parse comma seperated string, recurring group?

Question

I want to parse a string via RegEx (in real world my example is much more complex, else I would use split)

This:

import re 
regex="([a-z])(?:,([a-z]))*$" 
p=re.compile(regex)
print(p.findall("a,b,c,d,e"))

Outputs:

[('a', 'e')]

But I would expect:

['a','b','c','d','e']

As I did group up the [a-z] sequences.

How can I get this desired behaviour?