Fixed TYP of names argument of concat method and included test (pandas-dev#894)

* Fixed TYP of names argument of concat method and included test

Pointing to the issue pandas-dev#883

* Removed the duplicate test

Author: Aftabby

pandas-stubs/core/reshape/concat.pyi

@@ -32,7 +32,7 @@ def concat(
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,
@@ -46,7 +46,7 @@ def concat(  # type: ignore[overload-overlap] # pyright: ignore[reportOverlappin
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,
@@ -60,7 +60,7 @@ def concat(  # type: ignore[overload-overlap] # pyright: ignore[reportOverlappin
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,
@@ -74,7 +74,7 @@ def concat(
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,
@@ -88,7 +88,7 @@ def concat(  # type: ignore[overload-overlap]
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,
@@ -102,7 +102,7 @@ def concat(  # type: ignore[overload-overlap]
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,
@@ -119,7 +119,7 @@ def concat(
     ignore_index: bool = ...,
     keys: Iterable[HashableT2] = ...,
     levels: Sequence[list[HashableT3] | tuple[HashableT3, ...]] = ...,
-    names: list[HashableT4] = ...,
+    names: list[HashableT4] | None = ...,
     verify_integrity: bool = ...,
     sort: bool = ...,
     copy: bool = ...,

tests/test_pandas.py

@@ -98,6 +98,13 @@ def test_types_concat() -> None:
         ),
         pd.Series,
     )
+    check(
+        assert_type(
+            pd.concat([s, s2], keys=["first", "second"], names=None),
+            pd.Series,
+        ),
+        pd.Series,
+    )
 
     # Depends on the axis
     check(
@@ -140,6 +147,13 @@ def test_types_concat() -> None:
         ),
         pd.DataFrame,
     )
+    check(
+        assert_type(
+            pd.concat([df, df2], keys=["first", "second"], names=None),
+            pd.DataFrame,
+        ),
+        pd.DataFrame,
+    )
 
     check(
         assert_type(
@@ -189,6 +203,12 @@ def test_concat_args() -> None:
         ),
         pd.DataFrame,
     )
+    check(
+        assert_type(
+            pd.concat([df, df2], keys=["df1", "df2"], names=None), pd.DataFrame
+        ),
+        pd.DataFrame,
+    )
     check(
         assert_type(
             pd.concat([df, df2], keys=["df1", "df2"], names=[pd.Timedelta(1, "D")]),
@@ -248,6 +268,18 @@ def test_concat_args() -> None:
         ),
         pd.DataFrame,
     )
+    check(
+        assert_type(
+            pd.concat(
+                [df, df2, df, df2],
+                keys=[("foo", "one"), ("foo", "two"), ("baz", "one"), ("baz", "two")],
+                levels=levels,
+                names=None,
+            ),
+            pd.DataFrame,
+        ),
+        pd.DataFrame,
+    )
 
     check(
         assert_type(