Different number of matches from re.findall and re.split

MRAB python at mrabarnett.plus.com
Mon Jan 11 17:04:07 CET 2010

Jeremy wrote:
> On Jan 11, 8:44 am, Iain King <iaink... at gmail.com> wrote:
>> On Jan 11, 3:35 pm, Jeremy <jlcon... at gmail.com> wrote:
>>> Hello all,
>>> I am using re.split to separate some text into logical structures.
>>> The trouble is that re.split doesn't find everything while re.findall
>>> does; i.e.:
>>>> found = re.findall('^ 1', line, re.MULTILINE)
>>>> len(found)
>>>    6439
>>>> tables = re.split('^ 1', line, re.MULTILINE)
>>>> len(tables)
>>>> 1
>>> Can someone explain why these two commands are giving different
>>> results?  I thought I should have the same number of matches (or maybe
>>> different by 1, but not 6000!)
>>> Thanks,
>>> Jeremy
>> re.split doesn't take re.MULTILINE as a flag: it doesn't take any
>> flags. It does take a maxsplit parameter, which you are passing the
>> value of re.MULTILINE (which happens to be 8 in my implementation).
>> Since your pattern is looking for line starts, and your first line
>> presumably has more splits than the maxsplits you are specifying, your
>> re.split never finds more than 1.
> Yep.  Thanks for pointing that out.  I guess I just assumed that
> re.split was similar to re.search/match/findall in what it accepted as
> function parameters.  I guess I'll have to use a \n instead of a ^ for
> split.
You could use the .split method of a pattern object instead:

     tables = re.compile('^ 1', re.MULTILINE).split(line)

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