[New-bugs-announce] [issue28307] Accelerate 'string' % (value, ...) by using formatted string literals

Serhiy Storchaka report at bugs.python.org
Thu Sep 29 04:49:56 EDT 2016

New submission from Serhiy Storchaka:

For now using formatted string literals (PEP498) is the fastest way of formatting strings.

$ ./python -m perf timeit -s 'k = "foo"; v = "bar"' -- '"%s = %r" % (k, v)'
Median +- std dev: 2.27 us +- 0.20 us

$ ./python -m perf timeit -s 'k = "foo"; v = "bar"' -- 'f"{k!s} = {v!r}"'
Median +- std dev: 1.09 us +- 0.08 us

The compiler could translate C-style formatting with literal format string to the equivalent formatted string literal. The code '%s = %r' % (k, v) could be translated to

    t1 = k; t2 = v; f'{t1!r} = {t2!s}'; del t1, t2

or even simpler if k and v are initialized local variables.

$ ./python -m perf timeit -s 'k = "foo"; v = "bar"' -- 't1 = k; t2 = v; f"{t1!s} = {t2!r}"; del t1, t2'
Median +- std dev: 1.22 us +- 0.05 us

This is not easy issue and needs first implementing the AST optimizer.

components: Interpreter Core
messages: 277688
nosy: eric.smith, serhiy.storchaka
priority: low
severity: normal
status: open
title: Accelerate 'string' % (value, ...) by using formatted string literals
type: performance
versions: Python 3.7

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