python groupby behaviour?

Question

>>from itertools import groupby
>>keyfunc = lambda x : x > 500
>>obj = dict(groupby(range(1000), keyfunc))
>>list(obj[True])
         


        

Answer 1

The thing you are missing is, that the groupby-function iterates over your given range(1000), thus returning 1000 values. You are only saving the last one, in your case 999. What you have to do is, is to iterate over the return values and save them to your dictionary:

dictionary = {}
keyfunc = lambda x : x > 500
for k, g in groupby(range(1000), keyfunc):
    dictionary[k] = list(g)

So the you would get the expected output:

{False: [0, 1, 2, ...], True: [501, 502, 503, ...]}

For more information, see the Python docs about itertools groupby.