gh-529 Fixing Dataframe.insert (#543)

* Update test_frame.py

* Update frame.pyi

* Update test_frame.py

* Changed assert_type

* Update test_frame.py

* Update test_frame.py

Author: ramvikrams

pandas-stubs/core/frame.pyi

@@ -542,7 +542,7 @@ class DataFrame(NDFrame, OpsMixin):
         self,
         loc: int,
         column,
-        value: int | ListLike,
+        value: Scalar | ListLikeU | None,
         allow_duplicates: _bool = ...,
     ) -> None: ...
     def assign(self, **kwargs) -> DataFrame: ...

tests/test_frame.py

@@ -2410,3 +2410,12 @@ def test_in_columns() -> None:
     check(assert_type(df.loc[:, cols], pd.DataFrame), pd.DataFrame)
     check(assert_type(df[cols], pd.DataFrame), pd.DataFrame)
     check(assert_type(df.groupby(by=cols).sum(), pd.DataFrame), pd.DataFrame)
+
+
+def test_insert_newvalues() -> None:
+    df = pd.DataFrame({"a": [1, 2]})
+    ab = pd.DataFrame({"col1": [1, 2], "col2": [3, 4]})
+    ef = pd.DataFrame({"z": [4, 5, 6]})
+    assert assert_type(df.insert(loc=0, column="b", value=None), None) is None
+    assert assert_type(ab.insert(loc=0, column="newcol", value=[99, 99]), None) is None
+    assert assert_type(ef.insert(loc=0, column="g", value=4), None) is None