bug fix 54251 (#54388)

* bug fix 54251

* format

* whatsnew format

* PR comment fix

---------

Co-authored-by: tzehaoo <tzehao@intnt.ai>

Author: taytzehao

doc/source/whatsnew/v2.1.0.rst

@@ -675,6 +675,7 @@ Conversion
 - Bug in :meth:`DataFrame.info` raising  ``ValueError`` when ``use_numba`` is set (:issue:`51922`)
 - Bug in :meth:`DataFrame.insert` raising ``TypeError`` if ``loc`` is ``np.int64`` (:issue:`53193`)
 - Bug in :meth:`HDFStore.select` loses precision of large int when stored and retrieved (:issue:`54186`)
+- Bug in :meth:`Series.astype` not supporting ``object_`` (:issue:`54251`)
 
 Strings
 ^^^^^^^

pandas/core/dtypes/common.py

@@ -1634,7 +1634,13 @@ def pandas_dtype(dtype) -> DtypeObj:
     # also catch some valid dtypes such as object, np.object_ and 'object'
     # which we safeguard against by catching them earlier and returning
     # np.dtype(valid_dtype) before this condition is evaluated.
-    if is_hashable(dtype) and dtype in [object, np.object_, "object", "O"]:
+    if is_hashable(dtype) and dtype in [
+        object,
+        np.object_,
+        "object",
+        "O",
+        "object_",
+    ]:
         # check hashability to avoid errors/DeprecationWarning when we get
         # here and `dtype` is an array
         return npdtype

pandas/tests/dtypes/test_common.py

@@ -53,6 +53,7 @@ def test_invalid_dtype_error(self, box):
             np.float64,
             float,
             np.dtype("float64"),
+            "object_",
         ],
     )
     def test_pandas_dtype_valid(self, dtype):