Accelerate string.Template by using formatted string literals

[serhiy-storchaka]

BPO	28309
Nosy	@birkenfeld, @ericvsmith, @serhiy-storchaka
Files	faster_template.patch

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GitHub fields: ```python assignee = None closed_at = None created_at = labels = ['3.7', 'library', 'performance'] title = 'Accelerate string.Template by using formatted string literals' updated_at = user = 'https://github.com/serhiy-storchaka' ``` bugs.python.org fields: ```python activity = actor = 'serhiy.storchaka' assignee = 'none' closed = False closed_date = None closer = None components = ['Library (Lib)'] creation = creator = 'serhiy.storchaka' dependencies = [] files = ['44878'] hgrepos = [] issue_num = 28309 keywords = ['patch'] message_count = 1.0 messages = ['277690'] nosy_count = 3.0 nosy_names = ['georg.brandl', 'eric.smith', 'serhiy.storchaka'] pr_nums = [] priority = 'low' resolution = None stage = None status = 'open' superseder = None type = 'performance' url = 'https://bugs.python.org/issue28309' versions = ['Python 3.7'] ```

• PR: gh-99177

[serhiy-storchaka]

Proposed patch makes string.Template compiling template to formatted string literal. Since for now using formatted string literals is the fastest way of formatting strings, this significantly speeds up Template substitution.

$ ./python -m perf timeit -s 'from string import Template; s = Template("$who likes $what")' -- 's.substitute(who="tim", what="ham")'

Unpatched: Median +- std dev: 46.1 us +- 4.2 us Patched: Median +- std dev: 11.1 us +- 0.5 us

The drawback is that compiling template adds high overhead.

$ ./python -m perf timeit -s 'from string import Template' -- 's = Template("$who likes $what"); s.substitute(who="tim", what="ham")'

Unpatched: Median +- std dev: 51.7 us +- 1.5 us Patched: Median +- std dev: 672 us +- 38 us

The benefit of using compiled templates is achieved only if make at least 20 substitutions with the same template.

Third-party template engines can use the same approach in Python 3.6+.

[iritkatriel]

For this to go forward, the patch needs to be converted into a GitHub PR.

[delta1513]

From my own testing I noticed that the performance from the main branch vs the patch is identical and no improvements were made from this patch. Someone else may want to verify this in case I'm not exactly testing this correctly.

[akay25]

I'm available to help, can I take on this?

[u2rafi]

@akay25 there is already a pull request for it https://github.com/python/cpython/pull/99177