Question

I have a script that makes many calls to a dictionary using a key consisting of two variables. I know that my program will encounter the two variables again in the reverse order which makes storing the key as a tuple feasible. (Creating a matrix with the same labels for rows and columns)

Therefore, I was wondering if there was a performance difference in using a tuple over a frozenset for a dictionary key.

Answer 1

In a quick test, apparently it makes a negligible difference.

python -m timeit -s "keys = list(zip(range(10000), range(10, 10000)))" -s "values = range(10000)" -s "a=dict(zip(keys, values))" "for i in keys:" "  _ = a[i]"
1000 loops, best of 3: 855 usec per loop

python -m timeit -s "keys = [frozenset(i) for i in zip(range(10000), range(10, 10000))]" -s "values = range(10000)" -s "a=dict(zip(keys, values))" "for i in keys:" "  _ = a[i]"
1000 loops, best of 3: 848 usec per loop

I really would just go with what is best elsewhere in your code.