BUG/TST: PeriodArray.__setitem__ with slice and list-like value

pandas/core/arrays/period.py

@@ -347,7 +347,7 @@ def __repr__(self):
 
     def __setitem__(
             self,
-            key,   # type: Union[int, Sequence[int], Sequence[bool]]
+            key,   # type: Union[int, Sequence[int], Sequence[bool], slice]
             value  # type: Union[NaTType, Period, Sequence[Period]]
     ):
         # type: (...) -> None
@@ -357,11 +357,14 @@ def __setitem__(
         # ndarray[datetime64ns]. I think ndarray[int] / ndarray[str] won't
         # work, since the freq can't be inferred.
         if is_list_like(value):
-            if len(key) != len(value) and not com.is_bool_indexer(key):
+            is_slice = isinstance(key, slice)
+            if (not is_slice
+                    and len(key) != len(value)
+                    and not com.is_bool_indexer(key)):
                 msg = ("shape mismatch: value array of length '{}' does not "
                        "match indexing result of length '{}'.")
                 raise ValueError(msg.format(len(key), len(value)))
-            if len(key) == 0:
+            if not is_slice and len(key) == 0:
                 return
 
             value = period_array(value)

pandas/tests/extension/base/setitem.py

@@ -173,3 +173,13 @@ def test_setitem_tuple_index(self, data):
         expected = pd.Series(data.take([1, 1]), index=s.index)
         s[(0, 1)] = data[1]
         self.assert_series_equal(s, expected)
+
+    def test_setitem_slice_mismatch_length_raises(self, data):
+        arr = data[:5]
+        with pytest.raises(ValueError):
+            arr[:1] = arr[:2]
+
+    def test_setitem_slice_array(self, data):
+        arr = data[:5].copy()
+        arr[:5] = data[-5:]
+        self.assert_extension_array_equal(arr, data[-5:])