[Python-ideas] factory for efficient creation of many dicts with the same keys

[Sergey Fedoseev]

Hi all,

Sometimes you may need to create many dicts with the same keys, but different
values. For example, if you want to return data from DB as dicts.

I think that special type could be added to solve this task more effectively.
I created proof of concept for this and here's benchmarks:

# currently the fastest way to do it AFAIK
$ ./python -m timeit -s "nkeys = 5; nrows = 1000; rows = [(i,)*nkeys
for i in range(nrows)]; enumerated = list(enumerate(range(nkeys)))"
"for row in rows: {key: row[i] for i, key in enumerated}"
500 loops, best of 5: 645 usec per loop

$ ./python -m timeit -s "nkeys = 5; nrows = 1000; rows = [(i,)*nkeys
for i in range(nrows)]; factory = dict.factory(*range(nkeys)); from
itertools import starmap" "for d in starmap(factory, rows): d"
5000 loops, best of 5: 81.1 usec per loop

I'd like to write a patch if this idea will be accepted.