Fix full-day Durations collapsing to zero on PyPy

On PyPy, `Duration.total_seconds()` is overridden to compute the total from
`_days`/`_seconds`/`_microseconds`/etc. But `Duration.__new__` called
`self.total_seconds()` to derive `_total` *before* those attributes were
populated (they are still at their class defaults of 0 at that point), so the
computed total was 0 and the whole duration collapsed to `Duration()`. As a
result `duration(days=1).total_seconds()` returned 0 on PyPy.

Derive the total from `timedelta.total_seconds(self)` instead, which reads the
already-initialized underlying `timedelta` value and is independent of the
PyPy override. Behavior on CPython is unchanged (there the method is not
overridden, so both calls are equivalent).

Closes #876

Author: uttam12331

src/pendulum/duration.py

@@ -95,7 +95,14 @@ def __new__(
         )
 
         # Intuitive normalization
-        total = self.total_seconds() - (years * 365 + months * 30) * SECONDS_PER_DAY
+        # Use timedelta's own total_seconds() rather than self.total_seconds():
+        # on PyPy the latter is overridden to read _days/_seconds/... which are
+        # not populated yet at this point, which would zero out the duration
+        # (see issue #876).
+        total = (
+            timedelta.total_seconds(self)
+            - (years * 365 + months * 30) * SECONDS_PER_DAY
+        )
         self._total = total
 
         m = 1

tests/duration/test_construct.py

@@ -97,3 +97,16 @@ def test_float_years_and_months():
 
     with pytest.raises(ValueError):
         pendulum.duration(months=1.5)
+
+
+def test_new_does_not_depend_on_total_seconds_override(monkeypatch):
+    # __new__ must derive the duration's total from the underlying timedelta,
+    # not from a (possibly overridden) total_seconds(). On PyPy, total_seconds()
+    # is overridden to read _days/_seconds/... which are not populated yet during
+    # __new__, which zeroed out full-day durations (issue #876).
+    from pendulum.duration import Duration
+
+    monkeypatch.setattr(Duration, "total_seconds", lambda self: 0.0)
+
+    assert pendulum.duration(days=1)._total == 86400.0
+    assert pendulum.duration(hours=23)._total == 82800.0