[New-bugs-announce] [issue31614] can't list groupby generator without breaking the sub groups generators

[Loïc Le Loarer]

New submission from Loïc Le Loarer <loic.le-loarer at m4x.org>:

If I "list" the itertools groupby generator, then the sub generators of each groups are all empty except the last one.

import itertools as i
L = ['azerty','abcd','ac','aaa','z','baba','bitte','rhum','z','y']
g = list(i.groupby(L, lambda x: x[0]))
number_of_groups = len(g)
ans = 0
for k, v in g: # This doesn't work
#for k, v in i.groupby(L, lambda x: x[0]): # This works
    v = list(v)
    print(k,v,len(v))
    ans += 100*len(v)//number_of_groups
print(ans)
assert(ans == 163)
I don't understand why. Is my code broken ?

The need for saving the group generator first exists when I need the number of groups before walking thru the groups, like in the above example.

I have not been able to test to latest python versions, is the problem already fixed ?

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messages: 303180
nosy: Loïc Le Loarer
priority: normal
severity: normal
status: open
title: can't list groupby generator without breaking the sub groups generators
type: behavior
versions: Python 2.7, Python 3.5

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31614>
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