catch correct error in Timedelta sub

Author: patrickmckenna

pandas/_libs/tslibs/timedeltas.pyi

@@ -73,7 +73,6 @@ def array_to_timedelta64(
 ) -> np.ndarray: ...  # np.ndarray[m8ns]
 def parse_timedelta_unit(unit: str | None) -> UnitChoices: ...
 def delta_to_nanoseconds(delta: np.timedelta64 | timedelta | Tick) -> int: ...
-def calculate(op, left: int, right: int) -> int: ...
 
 class Timedelta(timedelta):
     min: ClassVar[Timedelta]

pandas/_libs/tslibs/timedeltas.pyx

@@ -684,13 +684,23 @@ def _op_unary_method(func, name):
     return f
 
 
-cpdef int64_t calculate(object op, int64_t a, int64_t b) except? -1:
+@cython.overflowcheck(True)
+cpdef int64_t _calculate(object op, int64_t a, int64_t b) except? -1:
+    """
+    Calculate op(a, b) and return the result. Raises OverflowError if either operand
+    or the result would overflow on conversion to int64_t.
+    """
+    return op(a, b)
+
+
+cpdef int64_t calculate(object op, object a, object b) except? -1:
     """
-    Calculate op(a, b) and return the result, or raise if the operation would overflow.
+    As above, but raises an OutOfBoundsTimedelta.
     """
+    cdef int64_t int_a, int_b
+
     try:
-        with cython.overflowcheck(True):
-            return op(a, b)
+        return _calculate(op, a, b)
     except OverflowError as ex:
         msg = f"outside allowed range [{TIMEDELTA_MIN_NS}ns, {TIMEDELTA_MAX_NS}ns]"
         raise OutOfBoundsTimedelta(msg) from ex

pandas/_libs/tslibs/timestamps.pyx

@@ -86,7 +86,7 @@ from pandas._libs.tslibs.np_datetime cimport (
     pydatetime_to_dt64,
 )
 
-from pandas._libs.tslibs.np_datetime import OutOfBoundsDatetime
+from pandas._libs.tslibs.np_datetime import OutOfBoundsDatetime, OutOfBoundsTimedelta
 
 from pandas._libs.tslibs.offsets cimport (
     BaseOffset,
@@ -431,14 +431,13 @@ cdef class _Timestamp(ABCTimestamp):
             # Timedelta
             try:
                 return Timedelta(self.value - other.value)
-            except (OverflowError, OutOfBoundsDatetime) as err:
-                if isinstance(other, _Timestamp):
-                    if both_timestamps:
-                        raise OutOfBoundsDatetime(
-                            "Result is too large for pandas.Timedelta. Convert inputs "
-                            "to datetime.datetime with 'Timestamp.to_pydatetime()' "
-                            "before subtracting."
-                        ) from err
+            except OutOfBoundsTimedelta as err:
+                if both_timestamps:
+                    raise OutOfBoundsTimedelta(
+                        "Result is too large for pandas.Timedelta. Convert inputs "
+                        "to datetime.datetime with 'Timestamp.to_pydatetime()' "
+                        "before subtracting."
+                    ) from err
                 # We get here in stata tests, fall back to stdlib datetime
                 #  method and return stdlib timedelta object
                 pass

pandas/tests/scalar/timedelta/conftest.py renamed to pandas/tests/scalar/conftest.py

@@ -72,17 +72,22 @@ def test_overflow_offset_raises(self):
         with pytest.raises(OverflowError, match=lmsg):
             stamp - offset_overflow
 
-    def test_overflow_timestamp_raises(self):
+    def test_sub_can_return_stdlib_timedelta_to_avoid_overflow(self, timedelta_overflow):
         # https://github.com/pandas-dev/pandas/issues/31774
-        msg = "Result is too large"
+        msg = "Result is too large for pandas.Timedelta"
         a = Timestamp("2101-01-01 00:00:00")
         b = Timestamp("1688-01-01 00:00:00")
 
-        with pytest.raises(OutOfBoundsDatetime, match=msg):
+        with pytest.raises(timedelta_overflow["expected_exception"], match=msg):
             a - b
 
-        # but we're OK for timestamp and datetime.datetime
-        assert (a - b.to_pydatetime()) == (a.to_pydatetime() - b)
+        # but we're OK for Timestamp and datetime.datetime
+        r0 = a - b.to_pydatetime()
+        r1 = a.to_pydatetime() - b
+        assert r0 == r1
+        assert isinstance(r0, timedelta)
+        assert isinstance(r1, timedelta)
+
 
     def test_delta_preserve_nanos(self):
         val = Timestamp(1337299200000000123)