Do not keep fractional remainders for months in precisedelta

Although 1 month is 30.5 days on average, we want 31 days to be one
month, and not remainder of 0.5 days which would not be intuitive.

Author: Daniel Gillet

src/humanize/time.py

@@ -379,7 +379,11 @@ def _quotient_and_remainder(
     if unit in suppress:
         return 0, value
 
-    return divmod(value, divisor)
+    # Convert the remainder back to integer is necessary for months. 1 month is 30.5
+    # days on average, but if we have 31 days, we want to count is as a whole month,
+    # and not as 1 month plus a remainder of 0.5 days.
+    q, r = divmod(value, divisor)
+    return q, int(r)
 
 
 def _suitable_minimum_unit(min_unit: Unit, suppress: Iterable[Unit]) -> Unit:
@@ -633,7 +637,7 @@ def precisedelta(
 def _rounding_by_fmt(format: str, value: float) -> float | int:
     """Round a number according to the string format provided.
 
-    The string format is the old printf-style String Formatting.
+    The string format is the old printf-style string formatting.
 
     If we are using a format which truncates the value, such as "%d" or "%i", the
     returned value will be of type `int`.

tests/test_time.py

@@ -563,14 +563,14 @@ def test_precisedelta_one_unit_enough(
             "minutes",
             "0 minutes",
         ),
-        (dt.timedelta(days=31), "seconds", "1 month and 12 hours"),
-        (dt.timedelta(days=32), "seconds", "1 month, 1 day and 12 hours"),
+        (dt.timedelta(days=31), "seconds", "1 month"),
+        (dt.timedelta(days=32), "seconds", "1 month and 1 day"),
         (dt.timedelta(days=62), "seconds", "2 months and 1 day"),
-        (dt.timedelta(days=92), "seconds", "3 months and 12 hours"),
-        (dt.timedelta(days=31), "days", "1 month and 0.50 days"),
-        (dt.timedelta(days=32), "days", "1 month and 1.50 days"),
+        (dt.timedelta(days=92), "seconds", "3 months"),
+        (dt.timedelta(days=31), "days", "1 month"),
+        (dt.timedelta(days=32), "days", "1 month and 1 day"),
         (dt.timedelta(days=62), "days", "2 months and 1 day"),
-        (dt.timedelta(days=92), "days", "3 months and 0.50 days"),
+        (dt.timedelta(days=92), "days", "3 months"),
     ],
 )
 def test_precisedelta_multiple_units(
@@ -620,19 +620,11 @@ def test_precisedelta_multiple_units(
             "5 days and 4.50 hours",
         ),
         (dt.timedelta(days=5, hours=4, seconds=30 * 60), "days", "%0.2f", "5.19 days"),
-        # 1 month is 30.5 days. Remaining 0.5 days is rounded down for both formats
+        # 1 month is 30.5 days but remainder is always rounded down.
         (dt.timedelta(days=31), "days", "%d", "1 month"),
         (dt.timedelta(days=31), "days", "%.0f", "1 month"),
-        # But adding a tiny amount will reveal a difference between %d and %.0f
-        # %d will truncate while %.0f will round to the nearest number.
-        (dt.timedelta(days=31.01), "days", "%d", "1 month"),
-        (dt.timedelta(days=31.01), "days", "%.0f", "1 month and 1 day"),
-        (dt.timedelta(days=31.99), "days", "%d", "1 month and 1 day"),
-        # 1 month is 30.5 days. Remaining 1.5 days is truncated for %d.
-        # For format %.0f, there is a tie, so it's rounded to the nearest even number,
-        # which is 2. See https://en.wikipedia.org/wiki/IEEE_754#Rounding_rules
         (dt.timedelta(days=32), "days", "%d", "1 month and 1 day"),
-        (dt.timedelta(days=32), "days", "%.0f", "1 month and 2 days"),
+        (dt.timedelta(days=32), "days", "%.0f", "1 month and 1 day"),
         (dt.timedelta(days=62), "days", "%d", "2 months and 1 day"),
         (dt.timedelta(days=92), "days", "%d", "3 months"),
         (dt.timedelta(days=120), "months", "%0.2f", "3.93 months"),