Fix scientific() sign and naturaldelta() negative durations

src/humanize/number.py

@@ -322,7 +322,7 @@ def scientific(value, precision=2):
         >>> scientific(int(500))
         '5.00 x 10²'
         >>> scientific(-1000)
-        '1.00 x 10⁻³'
+        '-1.00 x 10³'
         >>> scientific(1000, 1)
         '1.0 x 10³'
         >>> scientific(1000, 3)
@@ -357,18 +357,23 @@ def scientific(value, precision=2):
         "+": "⁺",
         "-": "⁻",
     }
-    negative = False
     try:
-        if "-" in str(value):
-            value = str(value).replace("-", "")
-            negative = True
-
         if isinstance(value, str):
             value = float(value)
+        else:
+            value = float(value)
+    except (ValueError, TypeError):
+        return value
+
+    if not math.isfinite(value):
+        return value
 
+    negative = value < 0
+    value = abs(value)
+
+    try:
         fmt = "{:.%se}" % str(int(precision))
         n = fmt.format(value)
-
     except (ValueError, TypeError):
         return value
 
@@ -380,13 +385,12 @@ def scientific(value, precision=2):
         part2 = part2.replace("+0", "")
 
     new_part2 = []
-    if negative:
-        new_part2.append(exponents["-"])
-
     for char in part2:
         new_part2.append(exponents[char])
 
     final_str = part1 + " x 10" + "".join(new_part2)
+    if negative:
+        final_str = "-" + final_str
 
     return final_str
 

src/humanize/time.py

@@ -135,8 +135,13 @@ def naturaldelta(
 
     use_months = months
 
-    seconds = abs(delta.seconds)
-    days = abs(delta.days)
+    # timedelta normalizes negatives as (days=-1, seconds=86395) for -5s;
+    # abs(days)/abs(seconds) separately would report that as "a day".
+    if delta.total_seconds() < 0:
+        delta = -delta
+
+    seconds = delta.seconds
+    days = delta.days
     years = days // 365
     days = days % 365
     months = int(days // 30.5)

tests/test_number.py

@@ -139,7 +139,7 @@ def test_fractional(test_input, expected):
     "test_args, expected",
     [
         ([1000], "1.00 x 10³"),
-        ([-1000], "1.00 x 10⁻³"),
+        ([-1000], "-1.00 x 10³"),
         ([5.5], "5.50 x 10⁰"),
         ([5781651000], "5.78 x 10⁹"),
         (["1000"], "1.00 x 10³"),
@@ -172,3 +172,13 @@ def test_scientific(test_args, expected):
 )
 def test_clamp(test_args, expected):
     assert humanize.clamp(*test_args) == expected
+
+
+def test_scientific_negative_and_nonfinite():
+    assert humanize.scientific(-1000) == "-1.00 x 10³"
+    assert humanize.scientific(-0.001) == "-1.00 x 10⁻³"
+    # non-finite values are returned unchanged (no cryptic split errors)
+    assert humanize.scientific(float("inf")) == float("inf")
+    assert humanize.scientific(float("-inf")) == float("-inf")
+    import math
+    assert math.isnan(humanize.scientific(float("nan")))

tests/test_time.py

@@ -623,3 +623,10 @@ def test_time_unit():
 
     with pytest.raises(TypeError):
         years < "foo"
+
+
+def test_naturaldelta_negative_duration():
+    """Negative durations must match the positive magnitude (not timedelta day borrow)."""
+    assert humanize.naturaldelta(-5) == humanize.naturaldelta(5)
+    assert humanize.naturaldelta(dt.timedelta(seconds=-5)) == "5 seconds"
+    assert humanize.naturaldelta(dt.timedelta(days=-1)) == "a day"