How do I use itertools.groupby()?

Question

I haven\'t been able to find an understandable explanation of how to actually use Python\'s itertools.groupby() function. What I\'m trying to do is this:

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Answer 1

WARNING:

The syntax list(groupby(...)) won't work the way that you intend. It seems to destroy the internal iterator objects, so using

for x in list(groupby(range(10))):
    print(list(x[1]))

will produce:

[]
[]
[]
[]
[]
[]
[]
[]
[]
[9]

Instead, of list(groupby(...)), try [(k, list(g)) for k,g in groupby(...)], or if you use that syntax often,

def groupbylist(*args, **kwargs):
    return [(k, list(g)) for k, g in groupby(*args, **kwargs)]

and get access to the groupby functionality while avoiding those pesky (for small data) iterators all together.