Re: [Python-ideas] Allow a group by operation for dict comprehension

June 29, 2018


      On Thu, Jun 28, 2018 at 5:12 PM Chris Barker via Python-ideas <
python-ideas@python.org> wrote:
...
In [97]: student_school_list
Out[97]:
[('Fred', 'SchoolA'),
 ('Bob', 'SchoolB'),
 ('Mary', 'SchoolA'),
 ('Jane', 'SchoolB'),
 ('Nancy', 'SchoolC')]
In [98]: result = defaultdict(list, student_by_school)
In [99]: result.items()
Out[99]: dict_items([('SchoolA', ['Fred', 'Mary']), ('SchoolB', ['Bob',
'Jane']), ('SchoolC', ['Nancy'])])
Wait, wha...

In [1]: from collections import defaultdict

In [2]: students = [('Fred', 'SchoolA'),
   ...:  ('Bob', 'SchoolB'),
   ...:  ('Mary', 'SchoolA'),
   ...:  ('Jane', 'SchoolB'),
   ...:  ('Nancy', 'SchoolC')]
   ...:

In [3]: defaultdict(list, students)
Out[3]:
defaultdict(list,
            {'Fred': 'SchoolA',
             'Bob': 'SchoolB',
             'Mary': 'SchoolA',
             'Jane': 'SchoolB',
             'Nancy': 'SchoolC'})

In [4]: defaultdict(list, students).items()
Out[4]: dict_items([('Fred', 'SchoolA'), ('Bob', 'SchoolB'), ('Mary',
'SchoolA'), ('Jane', 'SchoolB'), ('Nancy', 'SchoolC')])


I think you accidentally swapped variables there:
student_school_list
vs student_by_school

Re: [Python-ideas] Allow a group by operation for dict comprehension

Michael Selik