allow a dict in DataFrame.astype() (#449)

* allow a dict in DataFrame.astype()

* use mixed types in astype_dict test

Author: Dr-Irv

pandas-stubs/core/frame.pyi

@@ -1357,7 +1357,7 @@ class DataFrame(NDFrame, OpsMixin):
     ) -> DataFrame: ...
     def astype(
         self,
-        dtype: _str | Dtype | dict[_str, _str | Dtype] | Series,
+        dtype: _str | Dtype | Mapping[HashableT, _str | Dtype] | Series,
         copy: _bool = ...,
         errors: _str = ...,
     ) -> DataFrame: ...

tests/test_frame.py

@@ -2054,6 +2054,14 @@ def test_axes_as_tuple() -> None:
     check(assert_type(df, pd.DataFrame), pd.DataFrame)
 
 
+def test_astype_dict() -> None:
+    # GH 447
+    df = pd.DataFrame({"a": [1, 2, 3], 43: [4, 5, 6]})
+    columns_types = {"a": "int", 43: "float"}
+    df = df.astype(columns_types)
+    check(assert_type(df, pd.DataFrame), pd.DataFrame)
+
+
 def test_setitem_none() -> None:
     df = pd.DataFrame(
         {"A": [1, 2, 3], "B": ["abc", "def", "ghi"]}, index=["x", "y", "z"]