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metric: handle rounding carry at the quetta boundary #485

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metric: handle rounding carry at the quetta boundary #485

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af93d31
Handle metric rounding carry at the quetta boundary
mayur-dhavan Oct 25, 2026
b32f1f6
Add metric regression tests for the quetta rounding boundary
mayur-dhavan Oct 25, 2026
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6 changes: 5 additions & 1 deletion src/humanize/number.py
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Original file line number Diff line number Diff line change
Expand Up @@ -578,12 +578,16 @@ def metric(value: float, unit: str = "", precision: int = 3) -> str:
if exponent >= 33 or exponent < -30:
return scientific(value, precision - 1) + unit

original = value
old_bucket = exponent // 3 * 3
value /= 10**old_bucket
digits = int(max(0, precision - exponent % 3 - 1))
# Absorb a rounding carry (9.999 -> 10.0) by bumping the exponent.
if exponent < 30 and round(abs(value), digits) >= 10 ** (exponent % 3 + 1):
if round(abs(value), digits) >= 10 ** (exponent % 3 + 1):
exponent += 1
if exponent >= 33:
# Rounded past quetta: no larger prefix exists.
return scientific(original, precision - 1) + unit
new_bucket = exponent // 3 * 3
value /= 10 ** (new_bucket - old_bucket)
digits = int(max(0, precision - exponent % 3 - 1))
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6 changes: 6 additions & 0 deletions tests/test_number.py
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Expand Up @@ -332,6 +332,12 @@ def test_clamp(test_args: list[typing.Any], expected: str) -> None:
([1.235e29, "A"], "124 RA"),
([2.56e-30, "V"], "2.56 qV"),
([2.596e32, "F"], "260 QF"),
# Rounding carry at the quetta boundary (issue #423)
([9.996e30], "10.0 Q"),
([9.996e31], "100 Q"),
([9.996e32], "1.00 x 10\u00b3\u00b3"),
([9.999e-30], "10.0 q"),
([-9.996e31], "-100 Q"),
([1e50], "1.00 x 10⁵⁰"),
([1e-50], "1.00 x 10⁻⁵⁰"),
([-1500, "V"], "-1.50 kV"),
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