TYP: fix NDFrame.align

pandas/_typing.py

@@ -125,6 +125,9 @@
 # Series is passed into a function, a Series is always returned and if a DataFrame is
 # passed in, a DataFrame is always returned.
 NDFrameT = TypeVar("NDFrameT", bound="NDFrame")
+# same as NDFrameT, needed when binding two pairs of parameters to potentially
+# separate NDFrame-subclasses (see NDFrame.align)
+NDFrameTb = TypeVar("NDFrameTb", bound="NDFrame")
 
 NumpyIndexT = TypeVar("NumpyIndexT", np.ndarray, "Index")
 

pandas/core/frame.py

@@ -225,6 +225,7 @@
         Level,
         MergeHow,
         NaPosition,
+        NDFrameT,
         PythonFuncType,
         QuantileInterpolation,
         ReadBuffer,
@@ -4997,7 +4998,7 @@ def _reindex_multi(
     @doc(NDFrame.align, **_shared_doc_kwargs)
     def align(
         self,
-        other: DataFrame,
+        other: NDFrameT,
         join: AlignJoin = "outer",
         axis: Axis | None = None,
         level: Level = None,
@@ -5007,7 +5008,7 @@ def align(
         limit: int | None = None,
         fill_axis: Axis = 0,
         broadcast_axis: Axis | None = None,
-    ) -> DataFrame:
+    ) -> tuple[DataFrame, NDFrameT]:
         return super().align(
             other,
             join=join,
@@ -7771,9 +7772,7 @@ def to_series(right):
                     )
 
             left, right = left.align(
-                # error: Argument 1 to "align" of "DataFrame" has incompatible
-                # type "Series"; expected "DataFrame"
-                right,  # type: ignore[arg-type]
+                right,
                 join="outer",
                 axis=axis,
                 level=level,

pandas/core/generic.py

@@ -67,6 +67,7 @@
     Manager,
     NaPosition,
     NDFrameT,
+    NDFrameTb,
     RandomState,
     Renamer,
     Scalar,
@@ -198,7 +199,6 @@
     from pandas.core.indexers.objects import BaseIndexer
     from pandas.core.resample import Resampler
 
-
 # goal is to be able to define the docs close to function, while still being
 # able to share
 _shared_docs = {**_shared_docs}
@@ -9297,7 +9297,7 @@ def compare(
     @doc(**_shared_doc_kwargs)
     def align(
         self: NDFrameT,
-        other: NDFrameT,
+        other: NDFrameTb,
         join: AlignJoin = "outer",
         axis: Axis | None = None,
         level: Level = None,
@@ -9307,7 +9307,7 @@ def align(
         limit: int | None = None,
         fill_axis: Axis = 0,
         broadcast_axis: Axis | None = None,
-    ) -> NDFrameT:
+    ) -> tuple[NDFrameT, NDFrameTb]:
         """
         Align two objects on their axes with the specified join method.
 
@@ -9428,8 +9428,10 @@ def align(
                 df = cons(
                     {c: self for c in other.columns}, **other._construct_axes_dict()
                 )
-                return df._align_frame(
-                    other,
+                # error: Incompatible return value type (got "Tuple[DataFrame,
+                # DataFrame]", expected "Tuple[NDFrameT, NDFrameTb]")
+                return df._align_frame(  # type: ignore[return-value]
+                    other,  # type: ignore[arg-type]
                     join=join,
                     axis=axis,
                     level=level,
@@ -9446,7 +9448,9 @@ def align(
                 df = cons(
                     {c: other for c in self.columns}, **self._construct_axes_dict()
                 )
-                return self._align_frame(
+                # error: Incompatible return value type (got "Tuple[NDFrameT,
+                # DataFrame]", expected "Tuple[NDFrameT, NDFrameTb]")
+                return self._align_frame(  # type: ignore[return-value]
                     df,
                     join=join,
                     axis=axis,
@@ -9461,7 +9465,9 @@ def align(
         if axis is not None:
             axis = self._get_axis_number(axis)
         if isinstance(other, ABCDataFrame):
-            return self._align_frame(
+            # error: Incompatible return value type (got "Tuple[NDFrameT, DataFrame]",
+            # expected "Tuple[NDFrameT, NDFrameTb]")
+            return self._align_frame(  # type: ignore[return-value]
                 other,
                 join=join,
                 axis=axis,
@@ -9473,7 +9479,9 @@ def align(
                 fill_axis=fill_axis,
             )
         elif isinstance(other, ABCSeries):
-            return self._align_series(
+            # error: Incompatible return value type (got "Tuple[NDFrameT, Series]",
+            # expected "Tuple[NDFrameT, NDFrameTb]")
+            return self._align_series(  # type: ignore[return-value]
                 other,
                 join=join,
                 axis=axis,
@@ -9489,8 +9497,8 @@ def align(
 
     @final
     def _align_frame(
-        self,
-        other,
+        self: NDFrameT,
+        other: DataFrame,
         join: AlignJoin = "outer",
         axis: Axis | None = None,
         level=None,
@@ -9499,7 +9507,7 @@ def _align_frame(
         method=None,
         limit=None,
         fill_axis: Axis = 0,
-    ):
+    ) -> tuple[NDFrameT, DataFrame]:
         # defaults
         join_index, join_columns = None, None
         ilidx, iridx = None, None
@@ -9553,8 +9561,8 @@ def _align_frame(
 
     @final
     def _align_series(
-        self,
-        other,
+        self: NDFrameT,
+        other: Series,
         join: AlignJoin = "outer",
         axis: Axis | None = None,
         level=None,
@@ -9563,7 +9571,7 @@ def _align_series(
         method=None,
         limit=None,
         fill_axis: Axis = 0,
-    ):
+    ) -> tuple[NDFrameT, Series]:
         is_series = isinstance(self, ABCSeries)
         if copy and using_copy_on_write():
             copy = False
@@ -12798,8 +12806,8 @@ def _doc_params(cls):
 
 
 def _align_as_utc(
-    left: NDFrameT, right: NDFrameT, join_index: Index | None
-) -> tuple[NDFrameT, NDFrameT]:
+    left: NDFrameT, right: NDFrameTb, join_index: Index | None
+) -> tuple[NDFrameT, NDFrameTb]:
     """
     If we are aligning timezone-aware DatetimeIndexes and the timezones
     do not match, convert both to UTC.

pandas/core/series.py

@@ -166,6 +166,7 @@
         IndexLabel,
         Level,
         NaPosition,
+        NDFrameT,
         NumpySorter,
         NumpyValueArrayLike,
         QuantileInterpolation,
@@ -4571,7 +4572,7 @@ def _needs_reindex_multi(self, axes, method, level) -> bool:
     )
     def align(
         self,
-        other: Series,
+        other: NDFrameT,
         join: AlignJoin = "outer",
         axis: Axis | None = None,
         level: Level = None,
@@ -4581,7 +4582,7 @@ def align(
         limit: int | None = None,
         fill_axis: Axis = 0,
         broadcast_axis: Axis | None = None,
-    ) -> Series:
+    ) -> tuple[Series, NDFrameT]:
         return super().align(
             other,
             join=join,