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Perf: Optimize string concatenation in parse_uncertainty #112

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Perf: Optimize string concatenation in parse_uncertainty #112

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2 changes: 1 addition & 1 deletion periodictable/util.py
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ def parse_uncertainty(s):
# e.g., 23.0035(12) but not 23(1) or 23.0(1.0) or 23(1.0)
if '.' not in unc and '.' in value:
zeros = len(value.split('.')[1]) - len(unc)
unc = "0." + ("0"*zeros) + unc
unc = "".join(["0.", "0" * zeros, unc])
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@pkienzle pkienzle Feb 10, 2026 •
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On my machine the new version is slower. I also find it a little less readable.

value, unc = "3.1415913", "15"

%timeit zeros = len(value.split('.')[1]) - len(unc); full_unc = "0." + ("0"*zeros) + unc
132 ns ± 1.89 ns per loop (mean ± std. dev. of 7 runs, 10,000,000 loops each)

%timeit zeros = len(value.split('.')[1]) - len(unc); full_unc = "".join(["0.", "0" * zeros, unc])
148 ns ± 0.603 ns per loop (mean ± std. dev. of 7 runs, 10,000,000 loops each)

If you want to update the PR using f-strings that would be okay.

%timeit zeros = len(value.split('.')[1]) - len(unc); full_unc = f"0.{'0' * zeros}{unc}"
115 ns ± 0.0236 ns per loop (mean ± std. dev. of 7 runs, 10,000,000 loops each)

At 15 ns improvement per parsed number, I don't expect this to change startup times significantly, but every little bit helps.

[edit: changed "submit a new PR" to "update the PR"]
[edit: revised timing impact statement]

return float(value), float(unc)

# Plain value with no uncertainty
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