TYP: Remove _ensure_type (pandas-dev#32633)

* remove _ensure_type by TomAugspurger

* mypy fixup

* add test

* add whatsnew

Author: simonjayhawkins

doc/source/whatsnew/v1.0.2.rst

@@ -28,6 +28,7 @@ Fixed regressions
 - Fixed regression in the repr of an object-dtype :class:`Index` with bools and missing values (:issue:`32146`)
 - Fixed regression in :meth:`read_csv` in which the ``encoding`` option was not recognized with certain file-like objects (:issue:`31819`)
 - Fixed regression in :meth:`DataFrame.reindex` and :meth:`Series.reindex` when reindexing with (tz-aware) index and ``method=nearest`` (:issue:`26683`)
+- Fixed regression in :meth:`DataFrame.reindex_like` on a :class:`DataFrame` subclass raised an  ``AssertionError`` (:issue:`31925`)
 
 
 .. ---------------------------------------------------------------------------

pandas/core/base.py

@@ -9,7 +9,6 @@
 import numpy as np
 
 import pandas._libs.lib as lib
-from pandas._typing import T
 from pandas.compat import PYPY
 from pandas.compat.numpy import function as nv
 from pandas.errors import AbstractMethodError
@@ -87,15 +86,6 @@ def __sizeof__(self):
         # no memory_usage attribute, so fall back to object's 'sizeof'
         return super().__sizeof__()
 
-    def _ensure_type(self: T, obj) -> T:
-        """
-        Ensure that an object has same type as self.
-
-        Used by type checkers.
-        """
-        assert isinstance(obj, type(self)), type(obj)
-        return obj
-
 
 class NoNewAttributesMixin:
     """

pandas/core/frame.py

@@ -3637,7 +3637,7 @@ def reindex(self, *args, **kwargs) -> "DataFrame":
         # Pop these, since the values are in `kwargs` under different names
         kwargs.pop("axis", None)
         kwargs.pop("labels", None)
-        return self._ensure_type(super().reindex(**kwargs))
+        return super().reindex(**kwargs)
 
     def drop(
         self,
@@ -3955,8 +3955,8 @@ def replace(
 
     @Appender(_shared_docs["shift"] % _shared_doc_kwargs)
     def shift(self, periods=1, freq=None, axis=0, fill_value=None) -> "DataFrame":
-        return self._ensure_type(
-            super().shift(periods=periods, freq=freq, axis=axis, fill_value=fill_value)
+        return super().shift(
+            periods=periods, freq=freq, axis=axis, fill_value=fill_value
         )
 
     def set_index(
@@ -8409,14 +8409,12 @@ def isin(self, values) -> "DataFrame":
             from pandas.core.reshape.concat import concat
 
             values = collections.defaultdict(list, values)
-            return self._ensure_type(
-                concat(
-                    (
-                        self.iloc[:, [i]].isin(values[col])
-                        for i, col in enumerate(self.columns)
-                    ),
-                    axis=1,
-                )
+            return concat(
+                (
+                    self.iloc[:, [i]].isin(values[col])
+                    for i, col in enumerate(self.columns)
+                ),
+                axis=1,
             )
         elif isinstance(values, Series):
             if not values.index.is_unique:

pandas/core/generic.py

@@ -8442,9 +8442,9 @@ def _align_frame(
         )
 
         if method is not None:
-            left = self._ensure_type(
-                left.fillna(method=method, axis=fill_axis, limit=limit)
-            )
+            _left = left.fillna(method=method, axis=fill_axis, limit=limit)
+            assert _left is not None  # needed for mypy
+            left = _left
             right = right.fillna(method=method, axis=fill_axis, limit=limit)
 
         # if DatetimeIndex have different tz, convert to UTC
@@ -9977,9 +9977,9 @@ def pct_change(
         if fill_method is None:
             data = self
         else:
-            data = self._ensure_type(
-                self.fillna(method=fill_method, axis=axis, limit=limit)
-            )
+            _data = self.fillna(method=fill_method, axis=axis, limit=limit)
+            assert _data is not None  # needed for mypy
+            data = _data
 
         rs = data.div(data.shift(periods=periods, freq=freq, axis=axis, **kwargs)) - 1
         if freq is not None:

pandas/core/reshape/pivot.py

@@ -150,7 +150,9 @@ def pivot_table(
         table = table.sort_index(axis=1)
 
     if fill_value is not None:
-        table = table._ensure_type(table.fillna(fill_value, downcast="infer"))
+        _table = table.fillna(fill_value, downcast="infer")
+        assert _table is not None  # needed for mypy
+        table = _table
 
     if margins:
         if dropna:

pandas/io/formats/format.py

@@ -283,9 +283,7 @@ def _chk_truncate(self) -> None:
                 series = series.iloc[:max_rows]
             else:
                 row_num = max_rows // 2
-                series = series._ensure_type(
-                    concat((series.iloc[:row_num], series.iloc[-row_num:]))
-                )
+                series = concat((series.iloc[:row_num], series.iloc[-row_num:]))
             self.tr_row_num = row_num
         else:
             self.tr_row_num = None

pandas/tests/frame/indexing/test_indexing.py

@@ -1605,6 +1605,17 @@ def test_reindex_methods(self, method, expected_values):
         actual = df[::-1].reindex(target, method=switched_method)
         tm.assert_frame_equal(expected, actual)
 
+    def test_reindex_subclass(self):
+        # https://github.com/pandas-dev/pandas/issues/31925
+        class MyDataFrame(DataFrame):
+            pass
+
+        expected = DataFrame()
+        df = MyDataFrame()
+        result = df.reindex_like(expected)
+
+        tm.assert_frame_equal(result, expected)
+
     def test_reindex_methods_nearest_special(self):
         df = pd.DataFrame({"x": list(range(5))})
         target = np.array([-0.1, 0.9, 1.1, 1.5])