pp-str-plus-hot — str += vs str.join
Claim
Measured on this machine: primary hot case str_plus ratio before/after ~11.60× (faster after). Default severity stays off. Do not escalate to error from this fill alone.
How measured
- Harness:
packages/pyperf/examples/bench/evidence_pp.py - Protocol: warm=3; median of 9 rounds; GC/collect where applicable
- Raw lines:
pp-str-plus-hot.jsonl
Runtime (this evidence file)
| Field | Value |
|---|---|
| When | 2026-10-23 Asia/Shanghai (machine clock; JSONL ts is UTC) |
| Toolchain | CPython 3.15.1 |
Median after (str_join) | 0.243541 ms (ops=50000, ratio=1.000000) |
Median before (str_plus) | 2.824209 ms (ops=50000, ratio=11.596449) |
Median after (small_join) | 0.003750 ms (ops=100, ratio=1.000000) |
Median before (small_str_plus) | 0.007625 ms (ops=100, ratio=2.033404) |
| Primary ratio before/after | ~11.60× (str_plus) |
Direction and absolute ms are N/machine/opt-sensitive. Re-run the harness after toolchain or machine changes.
Lint mapping
pyperf-lint pp-str-plus-hot default stays off. Escalate recommended: no.
Limits
- Microbench; not an app profile.
- Small-N rows may sit near timer noise; prefer hot (non-small) cases for ratio claims.
- I/O rules (print/echo/puts/writeln) discard to
/dev/null— env-dependent.