Rule suggestion: recommend dict.fromkeys over comprehension #9592
Description
Replace
{elt: None for elt in foo}with
dict.fromkeys(foo)dict.fromkeys is more efficient and readable.
In [4]: import random
In [5]: choices = ("red", "green", "blue")
In [6]: dupes = [random.choice(choices) for _ in range(1000)]
In [7]: %timeit list({elt: None for elt in dupes})
18.8 µs ± 97.8 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)
In [8]: %timeit list(dict.fromkeys(dupes))
12.6 µs ± 49.9 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)
Efficiency boost tested on both Python 3.9 and 3.12.
Note: would have to skip this rule for mutable values (see #4613).