Regex that matches all week day's name in a string

Question

I want to match every week day in a string where all words are comma separated.

Examples: "mon, thu, fry" should be matched "mon, tue, sat" should be matched "" should not be matched "mon, tue, wed, thu, fri, sat, sun" should be matched "foo, bar" should not be matched

I came up with this regex but it matches only the string containing ALL week days:

^(mon|tue|wed|thu|fri|sat|sun)$

How can I match them "indipendently"?

I am using python3

You can use: ^(?:mon|tue|wed|thu|fri|sat|sun)(?:\s*,\s*(?:mon|tue|wed|thu|fri|sat|sun))*$ — anubhava
What happens if a string has days mixed with non day words, e.g. mon, foo ? — Tim Biegeleisen
Perhaps, ^(mon|tue|wed|thu|fri|sat|sun)(,\s*(mon|tue|wed|thu|fri|sat|sun))*$ — Wiktor Stribiżew
@TimBiegeleisen I should then handle that as an invalid string in my code. So the regex should not match anything... in an ideal world — refex
@refex - Check anubhava's comment. It handles the scenario which Tim is describing as well. — Utsav

Jan Jan · Accepted Answer · 2017-04-07T16:40:29

If you have the ability to use the newer regex module, you could use a recursive approach:

^((?:mon|tue|wed|thu|fri|sat|sun)(?:, )?)(?1)*$'

Python

import regex as re

string = """
mon, tue, fri
mon, tue, sat
mon, tue, wed, thu, fri, sat, sun
foo, bar
mon
tue
wed
mon, wed
"""

rx = re.compile(r'^((?:mon|tue|wed|thu|fri|sat|sun)(?:, )?)(?1)*$')
days = list(filter(lambda x: rx.match(x), string.split("\n")))
print(days)

Regex that matches all week day's name in a string

2 Answers