import re
regex = re.compile(r"""
(?(DEFINE)(?<cons>\b(?:
(?<x>\d*)
(?:(?<a0>0)|(?<a1>1)|(?<a2>2)|(?<a3>3)|(?<a4>4)
|(?<a5>5)|(?<a6>6)|(?<a7>7)|(?<a8>8))
(?:9(?= 9*,\g{x}\d (?<y>\g{y}?+ 0)))*
,\g{x}
(?(a0)1)(?(a1)2)(?(a2)3)(?(a3)4)(?(a4)5)
(?(a5)6)(?(a6)7)(?(a7)8)(?(a8)9)
(?(y)\g{y})
# handle the 999 => 1000 case separately
| (?:9(?= 9*,1 (?<z>\g{z}?+ 0)))+
,1\g{z}
)\b))
# list of two or more consecutive integers
(?=(?&cons))\d+
(?:,(?=(?&cons))\d+)*
,\d+
""", flags=re.VERBOSE)
test_str = ("0,1,2,3\n"
"8,9,10,11\n"
"1999,2000,2001\n"
"99,100,101\n\n"
"42\n"
" 3,2,1\n"
"1,2,4\n"
"10,11,13")
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