import re
regex = re.compile(r"""
^
(?#Block)
(?<block>(?:[a-z0-9]+)(?:-[a-z0-9]+)*)
(?:__
(?#Element)
(?<element>(?:[a-z0-9]+)(?:-[a-z0-9]+)*)
)?
(?:--
(?#Modifier)
(?<modifier>(?:[a-z0-9]+)(?:-[a-z0-9]+)*)
)?
$
""", flags=re.MULTILINE | re.VERBOSE)
test_str = "block__element--modifier"
matches = regex.finditer(test_str)
for match_num, match in enumerate(matches, start=1):
print(f"Match {match_num} was found at {match.start()}-{match.end()}: {match.group()}")
for group_num, group in enumerate(match.groups(), start=1):
print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Python, please visit: https://docs.python.org/3/library/re.html