Author serhiy.storchaka
Recipients eric.smith, serhiy.storchaka
Date 2016-09-29.08:49:55
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Message-id <1475138996.48.0.897803092987.issue28307@psf.upfronthosting.co.za>
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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.
History
Date User Action Args
2016-09-29 08:49:56serhiy.storchakasetrecipients: + serhiy.storchaka, eric.smith
2016-09-29 08:49:56serhiy.storchakasetmessageid: <1475138996.48.0.897803092987.issue28307@psf.upfronthosting.co.za>
2016-09-29 08:49:56serhiy.storchakalinkissue28307 messages
2016-09-29 08:49:55serhiy.storchakacreate