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Tested in 2.7 but possibly affects the other versions as well.
A real life example (note the first character '>' being lost):
>>> import re
>>> re.split(r'^>(.*)$', '>Homo sapiens catenin (cadherin-associated)')
produces:
['', 'Homo sapiens catenin (cadherin-associated)', '']
Expected (and IMHO most useful) behaviour would be for it to return:
['', '>Homo sapiens catenin (cadherin-associated)', '']
or (IMHO much less useful as one can already get this one just by adding external grouping parentheses and it is ):
['', '>Homo sapiens catenin (cadherin-associated)', 'Homo sapiens catenin (cadherin-associated)', '']
Not sure whether it can be changed in such a mature and widely used module without breaking compatibility but just adding a new optional parameter for deciding how re.split() deals with patterns containing grouping parentheses and making it default to the current behaviour would be very helpful.
Best Regards