Use `PyObject_CallMethodOneArg` in datetime `call_tzinfo_method`

[eendebakpt]

Feature or enhancement

Proposal:

The call_tzinfo_method() (invoked from tzinfo.utcoffset() and tzinfo.dst()) use:

offset = PyObject_CallMethod(tzinfo, name, "O", tzinfoarg);

On every call this parses the "O" format string, builds a temporary argument tuple, and rebuilds the method-name str (PyObject_GetAttrString). Switching to PyObject_CallMethodOneArg with interned strings improves performance.

Benchmarks

Wall-clock, PGO+LTO build

operation	before	after	speedup
astimezone() UTC→local	225.3 ns	124.3 ns	1.81×
timestamp()	461.5 ns	270.2 ns	1.71×
isoformat() (aware)	667.2 ns	542.1 ns	1.23×
utcoffset() (direct)	116.6 ns	48.4 ns	2.41×
now().isoformat() (control)	664.8 ns	681.8 ns	0.98×
tzname() (control)	48.8 ns	48.3 ns	1.01×

Benchmark script

"""Microbenchmark for datetime call_tzinfo_method (gh-150942)."""
import datetime as dt
import time
from datetime import timezone
from zoneinfo import ZoneInfo

ny = ZoneInfo("America/New_York")
utc_dt = dt.datetime(2024, 6, 7, 16, 30, tzinfo=timezone.utc)
ny_dt = dt.datetime(2024, 6, 7, 12, 30, tzinfo=ny)


def bench(fn, N=1_000_000, repeat=7):
    best = float("inf")
    for _ in range(repeat):
        start = time.perf_counter()
        for _ in range(N):
            fn()
        best = min(best, (time.perf_counter() - start) / N * 1e9)
    return best


CASES = {
    "astimezone() UTC->local": lambda: utc_dt.astimezone(ny),
    "timestamp()":             lambda: ny_dt.timestamp(),
    "isoformat()":             lambda: ny_dt.isoformat(),
    "utcoffset()":             lambda: ny_dt.utcoffset(),
    "now().isoformat()":       lambda: dt.datetime.now().isoformat(),  # naive: control
    "tzname()  [control]":     lambda: ny_dt.tzname(),
}

print(f"{'operation':<26}{'ns/op':>10}")
print("-" * 36)
for name, fn in CASES.items():
    print(f"{name:<26}{bench(fn):>9.1f}")

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-151059: Use PyObject_CallMethodOneArg in datetime call_tzinfo_method #151062