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gh-159702: Add fast-path for float in _json encoder - #159826
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Optimize json encoder for floats: up to 1.3x faster. Avoid creating a temporary Unicode object when writing the JSON representation of a float: decode directly the ASCII-encoded string (PyOS_double_to_string()) into the writer.
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Benchmark: import pyperf
runner = pyperf.Runner()
for list_len in (1, 10, 100, 1000):
runner.timeit(f'encode list of {list_len} floats',
setup=f'import json; L=[1.0] * {list_len}; dumps=json.dumps',
stmt='dumps(L)')Results:
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dolfinus
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Oct 20, 2026
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Modules/_json.c
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I compared the performance on jsonyx (because I didn't want to re-build CPython):
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Co-authored-by: Maxim Martynov <martinov_m_s_@mail.ru>
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Optimize json encoder for floats: up to 1.3x faster.
Avoid creating a temporary Unicode object when writing the JSON representation of a float: decode directly the ASCII-encoded string (PyOS_double_to_string()) into the writer.