Fixes for #16896(TimedeltaIndex indexing regression for strings)

doc/source/whatsnew/v0.21.0.txt

@@ -155,7 +155,7 @@ Indexing
 
 - When called with a null slice (e.g. ``df.iloc[:]``), the ``.iloc`` and ``.loc`` indexers return a shallow copy of the original object. Previously they returned the original object. (:issue:`13873`).
 - When called on an unsorted ``MultiIndex``, the ``loc`` indexer now will raise ``UnsortedIndexError`` only if proper slicing is used on non-sorted levels (:issue:`16734`).
-
+- Fixes regression in 0.20.3 when indexing with a string on a ``TimedeltaIndex`` (:issue:`16896`).
 
 I/O
 ^^^

pandas/core/dtypes/common.py

@@ -392,13 +392,15 @@ def is_timedelta64_dtype(arr_or_dtype):
     False
     >>> is_timedelta64_dtype(pd.Series([], dtype="timedelta64[ns]"))
     True
+    >>> is_timedelta64_dtype('0 days')
+    False
     """
 
     if arr_or_dtype is None:
         return False
     try:
         tipo = _get_dtype_type(arr_or_dtype)
-    except ValueError:
+    except:
         return False
     return issubclass(tipo, np.timedelta64)
 

pandas/tests/dtypes/test_common.py

@@ -199,12 +199,17 @@ def test_is_datetime64tz_dtype():
 
 def test_is_timedelta64_dtype():
     assert not com.is_timedelta64_dtype(object)
+    assert not com.is_timedelta64_dtype(None)
     assert not com.is_timedelta64_dtype([1, 2, 3])
     assert not com.is_timedelta64_dtype(np.array([], dtype=np.datetime64))
+    assert not com.is_timedelta64_dtype('0 days')
+    assert not com.is_timedelta64_dtype("0 days 00:00:00")
+    assert not com.is_timedelta64_dtype(["0 days 00:00:00"])
+    assert not com.is_timedelta64_dtype("NO DATE")
+
     assert com.is_timedelta64_dtype(np.timedelta64)
     assert com.is_timedelta64_dtype(pd.Series([], dtype="timedelta64[ns]"))
-
-    assert not com.is_timedelta64_dtype("0 days 00:00:00")
+    assert com.is_timedelta64_dtype(pd.to_timedelta(['0 days', '1 days']))
 
 
 def test_is_period_dtype():

pandas/tests/indexing/test_timedelta.py

@@ -5,7 +5,6 @@
 
 
 class TestTimedeltaIndexing(object):
-
     def test_boolean_indexing(self):
         # GH 14946
         df = pd.DataFrame({'x': range(10)})
@@ -40,3 +39,13 @@ def test_list_like_indexing(self, indexer, expected):
                                 dtype="int64")
 
         tm.assert_frame_equal(expected, df)
+
+    def test_string_indexing(self):
+        # GH 16896
+        df = pd.DataFrame({'x': range(3)},
+                          index=pd.to_timedelta(range(3), unit='days'))
+        expected = df.iloc[0]
+        sliced = df.loc['0 days']
+        tm.assert_series_equal(sliced, expected)
+
+        assert df.index.get_loc('0 days') == 0