BUG: Timedelta comparisons with very large pytimedeltas overflowing

doc/source/whatsnew/v2.0.0.rst

@@ -1190,6 +1190,7 @@ Timedelta
 - Bug in :func:`to_timedelta` raising error when input has nullable dtype ``Float64`` (:issue:`48796`)
 - Bug in :class:`Timedelta` constructor incorrectly raising instead of returning ``NaT`` when given a ``np.timedelta64("nat")`` (:issue:`48898`)
 - Bug in :class:`Timedelta` constructor failing to raise when passed both a :class:`Timedelta` object and keywords (e.g. days, seconds) (:issue:`48898`)
+- Bug in :class:`Timedelta` comparisons with very large ``datetime.timedelta`` objects incorrect raising ``OutOfBoundsTimedelta`` (:issue:`49021`)
 
 Timezones
 ^^^^^^^^^

pandas/_libs/tslibs/timedeltas.pyx

@@ -4,6 +4,10 @@ import warnings
 cimport cython
 from cpython.object cimport (
     Py_EQ,
+    Py_GE,
+    Py_GT,
+    Py_LE,
+    Py_LT,
     Py_NE,
     PyObject,
     PyObject_RichCompare,
@@ -1154,8 +1158,27 @@ cdef class _Timedelta(timedelta):
         if isinstance(other, _Timedelta):
             ots = other
         elif is_any_td_scalar(other):
-            ots = Timedelta(other)
-            # TODO: watch out for overflows
+            try:
+                ots = Timedelta(other)
+            except OutOfBoundsTimedelta as err:
+                # GH#49021 pytimedelta.max overflows
+                if not PyDelta_Check(other):
+                    # TODO: handle this case
+                    raise
+                ltup = (self.days, self.seconds, self.microseconds, self.nanoseconds)
+                rtup = (other.days, other.seconds, other.microseconds, 0)
+                if op == Py_EQ:
+                    return ltup == rtup
+                elif op == Py_NE:
+                    return ltup != rtup
+                elif op == Py_LT:
+                    return ltup < rtup
+                elif op == Py_LE:
+                    return ltup <= rtup
+                elif op == Py_GT:
+                    return ltup > rtup
+                elif op == Py_GE:
+                    return ltup >= rtup
 
         elif other is NaT:
             return op == Py_NE

pandas/tests/scalar/timedelta/test_arithmetic.py

@@ -966,6 +966,70 @@ def test_td_op_timedelta_timedeltalike_array(self, op, arr):
 
 
 class TestTimedeltaComparison:
+    def test_compare_pytimedelta_bounds(self):
+        # GH#49021 don't overflow on comparison with very large pytimedeltas
+
+        for unit in ["ns", "us"]:
+            tdmax = Timedelta.max.as_unit(unit).max
+            tdmin = Timedelta.min.as_unit(unit).min
+
+            assert tdmax < timedelta.max
+            assert tdmax <= timedelta.max
+            assert not tdmax > timedelta.max
+            assert not tdmax >= timedelta.max
+            assert tdmax != timedelta.max
+            assert not tdmax == timedelta.max
+
+            assert tdmin > timedelta.min
+            assert tdmin >= timedelta.min
+            assert not tdmin < timedelta.min
+            assert not tdmin <= timedelta.min
+            assert tdmin != timedelta.min
+            assert not tdmin == timedelta.min
+
+        # But the "ms" and "s"-reso bounds extend pass pytimedelta
+        for unit in ["ms", "s"]:
+            tdmax = Timedelta.max.as_unit(unit).max
+            tdmin = Timedelta.min.as_unit(unit).min
+
+            assert tdmax > timedelta.max
+            assert tdmax >= timedelta.max
+            assert not tdmax < timedelta.max
+            assert not tdmax <= timedelta.max
+            assert tdmax != timedelta.max
+            assert not tdmax == timedelta.max
+
+            assert tdmin < timedelta.min
+            assert tdmin <= timedelta.min
+            assert not tdmin > timedelta.min
+            assert not tdmin >= timedelta.min
+            assert tdmin != timedelta.min
+            assert not tdmin == timedelta.min
+
+    def test_compare_pytimedelta_bounds2(self):
+        # a pytimedelta outside the microsecond bounds
+        pytd = timedelta(days=999999999, seconds=86399)
+        # NB: np.timedelta64(td, "s"") incorrectly overflows
+        td64 = np.timedelta64(pytd.days, "D") + np.timedelta64(pytd.seconds, "s")
+        td = Timedelta(td64)
+        assert td.days == pytd.days
+        assert td.seconds == pytd.seconds
+
+        assert td == pytd
+        assert not td != pytd
+        assert not td < pytd
+        assert not td > pytd
+        assert td <= pytd
+        assert td >= pytd
+
+        td2 = td - Timedelta(seconds=1).as_unit("s")
+        assert td2 != pytd
+        assert not td2 == pytd
+        assert td2 < pytd
+        assert td2 <= pytd
+        assert not td2 > pytd
+        assert not td2 >= pytd
+
     def test_compare_tick(self, tick_classes):
         cls = tick_classes