Strange re behavior: normal?

Robin Munn rmunn at
Thu Aug 14 22:33:05 CEST 2003

How is re.split supposed to work? This wasn't at all what I expected:

[rmunn at localhost ~]$ python
Python 2.2.2 (#1, Jan 12 2003, 12:07:20)
[GCC 3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> re.split(r'\W+', 'a b c d')
['a', 'b', 'c', 'd']
>>> # Expected result.
>>> re.split(r'\b', 'a b c d')
['a b c d']
>>> # Huh?

Since \b matches the empty string, but only at the beginning and end of
a word, I would have expected re.split(r'\b', 'a b c d' to produce

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


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

But I didn't expect that re.split(r'\b', 'a b c d') would yield no splits
whatsoever. The module doc says "split(pattern, string[, maxsplit = 0]):
split string by the occurrences of pattern". re.findall() seems to think
that \b occurs eight times in 'a b c d':

>>> re.findall(r'\b', 'a b c d')
['', '', '', '', '', '', '', '']

So why doesn't re.split() think so? I'm puzzled.

Robin Munn <rmunn at> | | PGP key 0x6AFB6838
"Remember, when it comes to commercial TV, the program is not the product.
YOU are the product, and the advertiser is the customer." - Mark W. Schumann

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