Matt's idea leads to some speedups when implemented correctly (pardon me but I have no idea how to use pyperf):

list({}): Mean +- std dev: [orig] 109 ns +- 1 ns -> [modif] 103 ns +- 1 ns: 1.06x faster
list({1: 2}): Mean +- std dev: [orig] 125 ns +- 1 ns -> [modif] 118 ns +- 1 ns: 1.05x faster
list({(1, 2, 3): 4}): Mean +- std dev: [orig] 125 ns +- 1 ns -> [modif] 118 ns +- 1 ns: 1.05x faster
list((3, 3, 4)): Mean +- std dev: [orig] 89.2 ns +- 4.5 ns -> [modif] 82.9 ns +- 4.6 ns: 1.08x faster
list(()): Mean +- std dev: [orig] 70.1 ns +- 0.8 ns -> [modif] 65.5 ns +- 0.8 ns: 1.07x faster
list({0, 1, 2, ...}): Mean +- std dev: [orig] 74.7 us +- 3.6 us -> [modif] 67.6 us +- 1.6 us: 1.11x faster
list({9, 3}): Mean +- std dev: [orig] 131 ns +- 2 ns -> [modif] 126 ns +- 4 ns: 1.04x faster
list(set()): Mean +- std dev: [orig] 115 ns +- 6 ns -> [modif] 110 ns +- 2 ns: 1.05x faster
list([]): Mean +- std dev: [orig] 73.2 ns +- 5.5 ns -> [modif] 67.8 ns +- 3.4 ns: 1.08x faster
list([1, 2, 1, 1]): Mean +- std dev: [orig] 93.5 ns +- 9.8 ns -> [modif] 87.9 ns +- 8.6 ns: 1.06x faster
list([1, 2, 1, 2, 1, 2]): Mean +- std dev: [orig] 93.0 ns +- 3.1 ns -> [modif] 87.0 ns +- 2.7 ns: 1.07x faster

Benchmark hidden because not significant (3): list({0: 0, 1: ...}), list((4, 5, 1, ...)), list([4, 1, 3, ...])

Geometric mean: 1.05x faster

Changes compared here: https://github.com/python/cpython/compare/main...thatbirdguythatuknownot:patch-17