BUG: Allow addition of Timedelta to Timestamp interval

doc/source/whatsnew/v1.1.0.rst

@@ -363,6 +363,7 @@ Indexing
 - Bug in :class:`Index` constructor where an unhelpful error message was raised for ``numpy`` scalars (:issue:`33017`)
 - Bug in :meth:`DataFrame.lookup` incorrectly raising an ``AttributeError`` when ``frame.index`` or ``frame.columns`` is not unique; this will now raise a ``ValueError`` with a helpful error message (:issue:`33041`)
 - Bug in :meth:`DataFrame.iloc.__setitem__` creating a new array instead of overwriting ``Categorical`` values in-place (:issue:`32831`)
+- Bug in :class:`Interval` where a :class:`Timedelta` could not be added or subtracted from a :class:`Timestamp` interval (:issue:`32023`)
 
 Missing
 ^^^^^^^

pandas/_libs/interval.pyx

@@ -1,5 +1,6 @@
 import numbers
 from operator import le, lt
+from datetime import timedelta
 
 from cpython.object cimport (
     Py_EQ,
@@ -398,14 +399,14 @@ cdef class Interval(IntervalMixin):
         return f'{start_symbol}{left}, {right}{end_symbol}'
 
     def __add__(self, y):
-        if isinstance(y, numbers.Number):
+        if isinstance(y, (numbers.Number, Timedelta, timedelta)):
             return Interval(self.left + y, self.right + y, closed=self.closed)
-        elif isinstance(y, Interval) and isinstance(self, numbers.Number):
+        elif isinstance(y, Interval) and isinstance(self, numbers.Number, Timedelta, timedelta):
             return Interval(y.left + self, y.right + self, closed=y.closed)
         return NotImplemented
 
     def __sub__(self, y):
-        if isinstance(y, numbers.Number):
+        if isinstance(y, (numbers.Number, Timedelta, timedelta)):
             return Interval(self.left - y, self.right - y, closed=self.closed)
         return NotImplemented
 

pandas/tests/scalar/interval/test_arithmetic.py

@@ -0,0 +1,54 @@
+from datetime import timedelta
+
+from numpy import timedelta64
+import pytest
+
+from pandas import Interval, Timedelta, Timestamp
+
+
+@pytest.mark.parametrize("method", ["__add__", "__sub__"])
+@pytest.mark.parametrize(
+    "delta", [Timedelta(days=7), timedelta(7), timedelta64(7, "D")]
+)
+def test_timestamp_interval_add_subtract_timedelta(method, delta):
+    # https://github.com/pandas-dev/pandas/issues/32023
+    interval = Interval(
+        Timestamp("2017-01-01 00:00:00"), Timestamp("2018-01-01 00:00:00")
+    )
+
+    result = getattr(interval, method)(delta)
+
+    left = getattr(interval.left, method)(delta)
+    right = getattr(interval.right, method)(delta)
+    expected = Interval(left, right)
+
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "delta", [Timedelta(days=7), timedelta(7), timedelta64(7, "D")]
+)
+def test_timedelta_add_timestamp_interval(delta):
+    # https://github.com/pandas-dev/pandas/issues/32023
+    interval = Interval(
+        Timestamp("2017-01-01 00:00:00"), Timestamp("2018-01-01 00:00:00")
+    )
+
+    result = delta + interval
+
+    left = interval.left + delta
+    right = interval.right + delta
+    expected = Interval(left, right)
+
+    assert result == expected
+
+
+@pytest.mark.parametrize("method", ["__add__", "__sub__"])
+def test_numeric_interval_add_subtract_timedelta_raises(method):
+    # https://github.com/pandas-dev/pandas/issues/32023
+    interval = Interval(1, 2)
+    delta = Timedelta(days=7)
+
+    msg = "unsupported operand"
+    with pytest.raises(TypeError, match=msg):
+        getattr(interval, method)(delta)