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Fix metric() showing an extra significant digit on rounding carry #359

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Merged
hugovk merged 2 commits into from
Sep 16, 2026
+12 −2
Merged

Fix metric() showing an extra significant digit on rounding carry #359

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101c869
Fix metric() showing an extra significant digit on rounding carry
vidigoat Jul 25, 2026
408f28b
Less verbose comment
hugovk Sep 16, 2026
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5 changes: 3 additions & 2 deletions src/humanize/number.py
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Original file line number Diff line number Diff line change
Expand Up @@ -550,8 +550,9 @@ def metric(value: float, unit: str = "", precision: int = 3) -> str:
old_bucket = exponent // 3 * 3
value /= 10**old_bucket
digits = int(max(0, precision - exponent % 3 - 1))
if exponent < 30 and round(abs(value), digits) >= 1000:
exponent += 3 - exponent % 3
# Absorb a rounding carry (9.999 -> 10.0) by bumping the exponent.
if exponent < 30 and round(abs(value), digits) >= 10 ** (exponent % 3 + 1):
exponent += 1
new_bucket = exponent // 3 * 3
value /= 10 ** (new_bucket - old_bucket)
digits = int(max(0, precision - exponent % 3 - 1))
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9 changes: 9 additions & 0 deletions tests/test_number.py
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Expand Up @@ -270,6 +270,15 @@ def test_clamp(test_args: list[typing.Any], expected: str) -> None:
([1234.56], "1.23 k"),
([12345, "", 6], "12.3450 k"),
([200_000], "200 k"),
# Rounding that carries the mantissa up a power of ten within a
# bucket must not add an extra significant figure (issue: metric
# showed one digit too many for e.g. 9999 -> "10.00 k").
([9999], "10.0 k"),
([99999], "100 k"),
([9.99999], "10.0"),
([-9999], "-10.0 k"),
([9.999, "", 2], "10"),
([999.4], "999"),
([999.9, "V"], "1.00 kV"),
([999.99, "V"], "1.00 kV"),
([999_999, "V"], "1.00 MV"),
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