re.split(pattern, string, maxsplit=0, flags=0)
Split string by the occurrences of pattern. If capturing parentheses are used in pattern, then the text of all groups in the pattern are also returned as part of the resulting list. If maxsplit is nonzero, at most maxsplit splits occur, and the remainder of the string is returned as the final element of the list.
>>> re.split('\W+', 'Words, words, words.')
['Words', 'words', 'words', '']
>>> re.split('(\W+)', 'Words, words, words.')
['Words', ', ', 'words', ', ', 'words', '.', '']
>>> re.split('\W+', 'Words, words, words.', 1)
['Words', 'words, words.']
>>> re.split('[a-f]+', '0a3B9', flags=re.IGNORECASE)
['0', '3', '9']
If there are capturing groups in the separator and it matches at the start of the string, the result will start with an empty string. The same holds for the end of the string:
>>> re.split('(\W+)', '...words, words...')
['', '...', 'words', ', ', 'words', '...', '']
That way, separator components are always found at the same relative indices within the result list.
Note
split() doesn’t currently split a string on an empty pattern match. For example:
>>> re.split('x*', 'axbc')
['a', 'bc']
Even though 'x*' also matches 0 ‘x’ before ‘a’, between ‘b’ and ‘c’, and after ‘c’, currently these matches are ignored. The correct behavior (i.e. splitting on empty matches too and returning ['', 'a', 'b', 'c',
'']) will be implemented in future versions of Python, but since this is a backward incompatible change, a FutureWarning will be raised in the meanwhile.
Patterns that can only match empty strings currently never split the string. Since this doesn’t match the expected behavior, a ValueError will be raised starting from Python 3.5:
>>> re.split("^$", "foo\n\nbar\n", flags=re.M)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
...
ValueError: split() requires a non-empty pattern match.
Changed in version 3.1: Added the optional flags argument.
Changed in version 3.5: Splitting on a pattern that could match an empty string now raises a warning. Patterns that can only match empty strings are now rejected.
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