gh-118761: substitute re import in base64.b16decode for a more efficient alternative

[picnixz]

Benchmarks are on a RELEASE build (no PGO, no LTO).

See #128736 (comment) for the runtime performance improvements as well.

PR

$ ./python -I -X importtime -c 'import base64'
import time: self [us] | cumulative | imported package
...
import time:       179 |        179 | linecache
import time:       205 |        205 |     _struct
import time:       442 |        646 |   struct
import time:       227 |        227 |   binascii
import time:       298 |       1169 | base64

$ hyperfine --warmup 16 "./python -c 'import base64'"
Benchmark 1: ./python -c 'import base64'
  Time (mean ± σ):       5.7 ms ±   0.5 ms    [User: 4.8 ms, System: 1.1 ms]
  Range (min … max):     5.2 ms …  11.9 ms    455 runs

Main

$ ./python -I -X importtime -c 'import base64'
import time: self [us] | cumulative | imported package
...
import time:       180 |        180 | linecache
import time:       312 |        312 |       types
import time:      1609 |       1921 |     enum
import time:        87 |         87 |       _sre
import time:       250 |        250 |         re._constants
import time:       388 |        637 |       re._parser
import time:        89 |         89 |       re._casefix
import time:       339 |       1150 |     re._compiler
import time:       103 |        103 |         itertools
import time:        83 |         83 |         keyword
import time:        58 |         58 |           _operator
import time:       206 |        264 |         operator
import time:       129 |        129 |         reprlib
import time:        49 |         49 |         _collections
import time:       785 |       1411 |       collections
import time:        43 |         43 |       _functools
import time:       543 |       1997 |     functools
import time:       122 |        122 |     copyreg
import time:       826 |       6015 |   re
import time:       115 |        115 |     _struct
import time:        74 |        189 |   struct
import time:       122 |        122 |   binascii
import time:       279 |       6603 | base64

$ hyperfine --warmup 16 "./python -c 'import base64'"
Benchmark 1: ./python -c 'import base64'
  Time (mean ± σ):       9.5 ms ±   0.4 ms    [User: 8.2 ms, System: 1.3 ms]
  Range (min … max):     9.1 ms …  13.5 ms    295 runs

• Issue: Improve import time of various stdlib modules #118761

[picnixz]

@hugovk I'm requesting your review since you've commented on the issue. There are also #128732 and #128738 to review FYI.

[hugovk]

🚀

[AA-Turner]

Thanks!

A

[vstinner]

@AA-Turner merged commit bbd3300 into python:main Jan 14, 2025

FYI @picnixz was recently promoted as a core dev and so can merge his own changes.

[picnixz]

(I don't mind others merging my PRs by the way)

[chris-eibl]

and reduce the import time of :mod:base64 by up to six times.

9.5 ms down to 5.7 ms is impressive but not six times - rather 60%?

[picnixz]

hyperfine benchmarks also take into account interpreter's startup and so, while -X importtime only takes into account the time needed to import the module itself (hence the differences).

[chris-eibl]

Sure, my bad. Importtime itself is of course six times faster.

Thank you all for the great work here in cPython!