BUG: df.replace over pd.Period columns (pandas-dev#34904)

Author: samc1213

pandas/core/internals/blocks.py

@@ -10,6 +10,7 @@
 import pandas._libs.internals as libinternals
 from pandas._libs.internals import BlockPlacement
 from pandas._libs.tslibs import conversion
+from pandas._libs.tslibs.period import Period
 from pandas._libs.tslibs.timezones import tz_compare
 from pandas._typing import ArrayLike, Scalar
 from pandas.util._validators import validate_bool_kwarg
@@ -1975,6 +1976,18 @@ def external_values(self):
         return self.values.astype(object)
 
 
+class PeriodExtensionBlock(ObjectValuesExtensionBlock):
+    """
+    Used by PeriodArray to ensure proper type conversions
+    """
+
+    def _can_hold_element(self, element: Any) -> bool:
+        tipo = maybe_infer_dtype_type(element)
+        if tipo is not None:
+            return issubclass(tipo.type, Period)
+        return isinstance(element, Period)
+
+
 class NumericBlock(Block):
     __slots__ = ()
     is_numeric = True
@@ -2747,8 +2760,10 @@ def get_block_type(values, dtype=None):
         cls = DatetimeBlock
     elif is_datetime64tz_dtype(values.dtype):
         cls = DatetimeTZBlock
-    elif is_interval_dtype(dtype) or is_period_dtype(dtype):
+    elif is_interval_dtype(dtype):
         cls = ObjectValuesExtensionBlock
+    elif is_period_dtype(dtype):
+        cls = PeriodExtensionBlock
     elif is_extension_array_dtype(values.dtype):
         cls = ExtensionBlock
     elif issubclass(vtype, np.floating):

pandas/core/internals/managers.py

@@ -47,6 +47,7 @@
     DatetimeTZBlock,
     ExtensionBlock,
     ObjectValuesExtensionBlock,
+    PeriodExtensionBlock,
     extend_blocks,
     get_block_type,
     make_block,
@@ -1743,6 +1744,14 @@ def form_blocks(arrays, names: Index, axes) -> List[Block]:
 
         blocks.extend(external_blocks)
 
+    if len(items_dict["PeriodExtensionBlock"]):
+        external_blocks = [
+            make_block(array, klass=PeriodExtensionBlock, placement=i)
+            for i, _, array in items_dict["PeriodExtensionBlock"]
+        ]
+
+        blocks.extend(external_blocks)
+
     if len(extra_locs):
         shape = (len(extra_locs),) + tuple(len(x) for x in axes[1:])
 

pandas/tests/frame/methods/test_replace.py

@@ -1517,9 +1517,6 @@ def test_replace_with_duplicate_columns(self, replacement):
 
         tm.assert_frame_equal(result, expected)
 
-    @pytest.mark.xfail(
-        reason="replace() changes dtype from period to object, see GH34871", strict=True
-    )
     def test_replace_period_ignore_float(self):
         """
         Regression test for GH#34871: if df.replace(1.0, 0.0) is called on a df