Python – Dict.setdefault inserts a sort into the list

I was wondering if there was a way to append to sorted dictionary list fields using lambda-like styles.

Example:

a = {}
a.setdefault("foo", []).append(2)
a.setdefault("foo", []).append(1)
{'foo': [2, 1]}

Is there a way to insert in sort order like using a["foo"].bisect.insort(a, -1) so that I don’t need to call sort later?

Everything you need is in Python’s standard library:

import bisect
from collections import defaultdict

def add(dd, key, value):
    bisect.insort_left(dd[key], value)

a = defaultdict(list)
add(a, "foo", 3)
add(a, "foo", 2)
add(a, "foo", 1)
add(a, "foo", 3)
add(a, "foo", 2)
add(a, "foo", 1)

assert a["foo"] == sorted(a["foo"])
print(a)

If you want a lambda:

add = lambda dd, key, value: bisect.insort_left(dd[key], value)

In terms of performance, using the sort runtime afterwards should be faster than using bisect.insort_left. In both cases, the runtime complexity is O(n log n), but the function call overhead should result in different absolute run times.