A problem with itertools.groupby

[ast]

Python 3.9.9

Hello

I have some troubles with groupby from itertools

from itertools import groupby

for k, grp in groupby("aahfffddssssnnb"):
     print(k, list(grp))
     print(k, list(grp))

a ['a', 'a']
a []
h ['h']
h []
f ['f', 'f', 'f']
f []
d ['d', 'd']
d []
s ['s', 's', 's', 's']
s []
n ['n', 'n']
n []
b ['b']
b []

It works as expected.
itertools._grouper objects are probably iterators
so they provide their datas only once. OK

but:

li = [grp for k, grp in groupby("aahfffddssssnnb")]
list(li[0])

[]

list(li[1])

[]

It seems empty ... I don't understand why, this is
the first read of an iterator, it should provide its
data.

This one works:

["".join(grp) for k, grp in groupby("aahfffddssssnnb")]

['aa', 'h', 'fff', 'dd', 'ssss', 'nn', 'b']

regards