BUG: wrong exception when slicing on TimedeltaIndex (pandas-dev#41821)

Author: jbrockmendel

doc/source/whatsnew/v1.3.0.rst

@@ -1025,6 +1025,7 @@ Indexing
 - Bug in :meth:`PeriodIndex.get_loc` failing to raise a ``KeyError`` when given a :class:`Period` with a mismatched ``freq`` (:issue:`41670`)
 - Bug ``.loc.__getitem__`` with a :class:`UInt64Index` and negative-integer keys raising ``OverflowError`` instead of ``KeyError`` in some cases, wrapping around to positive integers in others (:issue:`41777`)
 - Bug in :meth:`Index.get_indexer` failing to raise ``ValueError`` in some cases with invalid ``method``, ``limit``, or ``tolerance`` arguments (:issue:`41918`)
+- Bug when slicing a :class:`Series` or :class:`DataFrame` with a :class:`TimedeltaIndex` when passing an invalid string raising ``ValueError`` instead of a ``TypeError`` (:issue:`41821`)
 
 Missing
 ^^^^^^^

pandas/core/indexes/datetimelike.py

@@ -26,7 +26,10 @@
     Resolution,
     Tick,
 )
-from pandas._typing import Callable
+from pandas._typing import (
+    Callable,
+    final,
+)
 from pandas.compat.numpy import function as nv
 from pandas.util._decorators import (
     Appender,
@@ -400,6 +403,7 @@ def _validate_partial_date_slice(self, reso: Resolution):
     def _parsed_string_to_bounds(self, reso: Resolution, parsed: datetime):
         raise NotImplementedError
 
+    @final
     def _partial_date_slice(
         self,
         reso: Resolution,

pandas/core/indexes/period.py

@@ -31,7 +31,6 @@
 
 from pandas.core.dtypes.common import (
     is_datetime64_any_dtype,
-    is_float,
     is_integer,
     pandas_dtype,
 )
@@ -489,13 +488,14 @@ def _maybe_cast_slice_bound(self, label, side: str, kind=lib.no_default):
         elif isinstance(label, str):
             try:
                 parsed, reso_str = parse_time_string(label, self.freq)
-                reso = Resolution.from_attrname(reso_str)
-                bounds = self._parsed_string_to_bounds(reso, parsed)
-                return bounds[0 if side == "left" else 1]
             except ValueError as err:
                 # string cannot be parsed as datetime-like
                 raise self._invalid_indexer("slice", label) from err
-        elif is_integer(label) or is_float(label):
+
+            reso = Resolution.from_attrname(reso_str)
+            lower, upper = self._parsed_string_to_bounds(reso, parsed)
+            return lower if side == "left" else upper
+        elif not isinstance(label, self._data._recognized_scalars):
             raise self._invalid_indexer("slice", label)
 
         return label

pandas/core/indexes/timedeltas.py

@@ -196,12 +196,16 @@ def _maybe_cast_slice_bound(self, label, side: str, kind=lib.no_default):
         self._deprecated_arg(kind, "kind", "_maybe_cast_slice_bound")
 
         if isinstance(label, str):
-            parsed = Timedelta(label)
-            lbound = parsed.round(parsed.resolution_string)
-            if side == "left":
-                return lbound
-            else:
-                return lbound + to_offset(parsed.resolution_string) - Timedelta(1, "ns")
+            try:
+                parsed = Timedelta(label)
+            except ValueError as err:
+                # e.g. 'unit abbreviation w/o a number'
+                raise self._invalid_indexer("slice", label) from err
+
+            # The next two lines are analogous to DTI/PI._parsed_str_to_bounds
+            lower = parsed.round(parsed.resolution_string)
+            upper = lower + to_offset(parsed.resolution_string) - Timedelta(1, "ns")
+            return lower if side == "left" else upper
         elif not isinstance(label, self._data._recognized_scalars):
             raise self._invalid_indexer("slice", label)
 

pandas/tests/indexes/timedeltas/test_indexing.py

@@ -291,3 +291,52 @@ def test_take_fill_value(self):
         msg = "index -5 is out of bounds for (axis 0 with )?size 3"
         with pytest.raises(IndexError, match=msg):
             idx.take(np.array([1, -5]))
+
+
+class TestMaybeCastSliceBound:
+    @pytest.fixture(params=["increasing", "decreasing", None])
+    def monotonic(self, request):
+        return request.param
+
+    @pytest.fixture
+    def tdi(self, monotonic):
+        tdi = timedelta_range("1 Day", periods=10)
+        if monotonic == "decreasing":
+            tdi = tdi[::-1]
+        elif monotonic is None:
+            taker = np.arange(10, dtype=np.intp)
+            np.random.shuffle(taker)
+            tdi = tdi.take(taker)
+        return tdi
+
+    def test_maybe_cast_slice_bound_invalid_str(self, tdi):
+        # test the low-level _maybe_cast_slice_bound and that we get the
+        #  expected exception+message all the way up the stack
+        msg = (
+            "cannot do slice indexing on TimedeltaIndex with these "
+            r"indexers \[foo\] of type str"
+        )
+        with pytest.raises(TypeError, match=msg):
+            tdi._maybe_cast_slice_bound("foo", side="left")
+        with pytest.raises(TypeError, match=msg):
+            tdi.get_slice_bound("foo", side="left")
+        with pytest.raises(TypeError, match=msg):
+            tdi.slice_locs("foo", None, None)
+
+    def test_slice_invalid_str_with_timedeltaindex(
+        self, tdi, frame_or_series, indexer_sl
+    ):
+        obj = frame_or_series(range(10), index=tdi)
+
+        msg = (
+            "cannot do slice indexing on TimedeltaIndex with these "
+            r"indexers \[foo\] of type str"
+        )
+        with pytest.raises(TypeError, match=msg):
+            indexer_sl(obj)["foo":]
+        with pytest.raises(TypeError, match=msg):
+            indexer_sl(obj)["foo":-1]
+        with pytest.raises(TypeError, match=msg):
+            indexer_sl(obj)[:"foo"]
+        with pytest.raises(TypeError, match=msg):
+            indexer_sl(obj)[tdi[0] : "foo"]