[cmaloney]

Since 3.11 added bytes.__bytes__, bytes(b) for an exact bytes binds and calls that method only to get b back. Return an exact bytes argument directly, like PyObject_Bytes() and PyBytes_FromObject() do, and skip the lookup, which always misses, for an exact int.

How bytes(x) resolves is unchanged: both types are immutable, so the skipped lookup and call could only ever produce the same result, and subclasses, including bool, still look up __bytes__ first. These cases just get there faster.

Could inline the PyLong as another if but that makes a bigger diff and the runtime is very close to just adding the !PyLong_CheckExact case.

pyperf, PGO+LTO, interleaved A/B on 19270d3 (A/A spread <= 1.05x):

Benchmark	main	patch
bytes(b)	28.5 ns	12.8 ns: 2.22x faster
Sub(b)	51.7 ns	36.0 ns: 1.44x faster
bytes(16)	23.5 ns	21.0 ns: 1.12x faster
bytes(hb)	38.7 ns	38.0 ns: 1.02x faster
bytes(s, 'ascii')	26.5 ns	27.1 ns: 1.02x slower
bytes()	10.7 ns	11.1 ns: 1.03x slower

Not significant: bytes(ba), bytes(l), bytes(mv). The small slowdowns (1.02-1.03x) are within the noise on my machine.

import pyperf

runner = pyperf.Runner()
for stmt in ["bytes(b)", "bytes(16)", "bytes(ba)", "bytes(mv)", "bytes(l)",
             "bytes(s, 'ascii')", "bytes(hb)", "Sub(b)", "bytes()"]:
    runner.timeit(stmt, stmt,
                  "b = b'abcdefghijklmnop'; ba = bytearray(b); mv = memoryview(b); "
                  "l = list(range(16)); s = 'abcdefghijklmnop'\n"
                  "class Sub(bytes): pass\n"
                  "class HB:\n    def __bytes__(self): return b\n"
                  "hb = HB()")

• Issue: Skip the __bytes__ lookup in bytes() for exact bytes and int #160931