From b9c19662891687c27cdee15debcf1ac4a7d099fc Mon Sep 17 00:00:00 2001
From: santhreal <64453045+santhreal@users.noreply.github.com>
Date: Thu, 16 Jul 2026 20:57:19 -0700
Subject: [PATCH 1/2] Clamp negative precision in scientific()

scientific() built its format spec as f"{{:.{int(precision)}e}}", so a
negative precision produced an invalid spec ("{:.-1e}") and raised
ValueError. This is reachable from the public API through metric(value,
precision=0): for magnitudes that fall back to scientific notation,
metric() calls scientific(value, precision - 1), i.e. scientific(value,
-1). PR #159 added the same max(0, ...) clamp to metric()'s main path but
not to scientific(). Clamp the precision to zero.
---
 src/humanize/number.py | 3 ++-
 tests/test_number.py   | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/humanize/number.py b/src/humanize/number.py
index 2fb22c6..d6f7e9e 100644
--- a/src/humanize/number.py
+++ b/src/humanize/number.py
@@ -416,7 +416,8 @@ def scientific(value: NumberOrString, precision: int = 2) -> str:
             return _format_not_finite(value)
     except (ValueError, TypeError):
         return str(value)
-    fmt = f"{{:.{int(precision)}e}}"
+    # max(0): a negative precision builds an invalid format spec ("{:.-1e}").
+    fmt = f"{{:.{max(0, int(precision))}e}}"
     n = fmt.format(value)
     part1, part2 = n.split("e")
     # Normalise exponent: int() strips the "+" sign and leading zeros,
diff --git a/tests/test_number.py b/tests/test_number.py
index 78639c3..a9ac79d 100644
--- a/tests/test_number.py
+++ b/tests/test_number.py
@@ -218,6 +218,10 @@ def test_fractional(test_input: float | str, expected: str) -> None:
         ([-math.inf], "-Inf"),
         (["nan"], "NaN"),
         (["-inf"], "-Inf"),
+        # Negative precision clamps to zero instead of building an invalid spec.
+        ([1e300, -1], "1 x 10³⁰⁰"),
+        ([1e300, -5], "1 x 10³⁰⁰"),
+        ([-1000, -1], "-1 x 10³"),
     ],
 )
 def test_scientific(test_args: list[typing.Any], expected: str) -> None:
@@ -310,6 +314,11 @@ def test_clamp(test_args: list[typing.Any], expected: str) -> None:
         ([math.nan, "m"], "NaN"),
         ([math.inf], "+Inf"),
         ([-math.inf], "-Inf"),
+        # precision=0 on a scientific-fallback magnitude passed -1 to scientific(); see #159.
+        ([1e300, "m", 0], "1 x 10³⁰⁰m"),
+        ([-1e300, "m", 0], "-1 x 10³⁰⁰m"),
+        ([1e-300, "m", 0], "1 x 10⁻³⁰⁰m"),
+        ([1e40, "", 0], "1 x 10⁴⁰"),
     ],
     ids=str,
 )

From c6782b5dffccba33e623c7cfbfa05f14cea1a905 Mon Sep 17 00:00:00 2001
From: santhreal <64453045+santhreal@users.noreply.github.com>
Date: Sat, 18 Jul 2026 16:28:24 -0700
Subject: [PATCH 2/2] Fix E501 on scientific precision=0 test comment.

---
 tests/test_number.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_number.py b/tests/test_number.py
index a9ac79d..0d1483f 100644
--- a/tests/test_number.py
+++ b/tests/test_number.py
@@ -314,7 +314,7 @@ def test_clamp(test_args: list[typing.Any], expected: str) -> None:
         ([math.nan, "m"], "NaN"),
         ([math.inf], "+Inf"),
         ([-math.inf], "-Inf"),
-        # precision=0 on a scientific-fallback magnitude passed -1 to scientific(); see #159.
+        # precision=0 scientific fallback used to pass -1 into scientific(); see #159.
         ([1e300, "m", 0], "1 x 10³⁰⁰m"),
         ([-1e300, "m", 0], "-1 x 10³⁰⁰m"),
         ([1e-300, "m", 0], "1 x 10⁻³⁰⁰m"),