TYP: Add FrameORSeries to NDFrame

Author: topper-123

pandas/core/base.py

@@ -37,6 +37,10 @@
 from pandas.core.construction import create_series_with_explicit_dtype
 import pandas.core.nanops as nanops
 
+
+from pandas._typing import T
+
+
 _shared_docs: Dict[str, str] = dict()
 _indexops_doc_kwargs = dict(
     klass="IndexOpsMixin",
@@ -87,6 +91,14 @@ def __sizeof__(self):
         # 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:
     """Mixin which prevents adding new attributes.