Fix issue 27395

Author: inmoonlight

doc/source/whatsnew/v0.25.1.rst

@@ -32,7 +32,7 @@ Categorical
 Datetimelike
 ^^^^^^^^^^^^
 - Bug in :func:`to_datetime` where passing a timezone-naive :class:`DatetimeArray` or :class:`DatetimeIndex` and ``utc=True`` would incorrectly return a timezone-naive result (:issue:`27733`)
--
+- Bug in :func:`maybe_cast_to_datetime` where converting a `np.datetime64` to `datetime64[D]` raise `TypeError` (:issue: `27395`)
 -
 -
 

pandas/core/dtypes/cast.py

@@ -1026,7 +1026,7 @@ def maybe_cast_to_datetime(value, dtype, errors="raise"):
             )
 
             if is_datetime64 and not is_dtype_equal(dtype, _NS_DTYPE):
-                if dtype.name in ("datetime64", "datetime64[ns]"):
+                if dtype.name in ("datetime64", "datetime64[ns]", "datetime64[D]"):
                     if dtype.name == "datetime64":
                         raise ValueError(msg.format(dtype=dtype.name))
                     dtype = _NS_DTYPE
@@ -1044,7 +1044,7 @@ def maybe_cast_to_datetime(value, dtype, errors="raise"):
                     value = [value]
 
             elif is_timedelta64 and not is_dtype_equal(dtype, _TD_DTYPE):
-                if dtype.name in ("timedelta64", "timedelta64[ns]"):
+                if dtype.name in ("timedelta64", "timedelta64[ns]", "timedelta64[D]"):
                     if dtype.name == "timedelta64":
                         raise ValueError(msg.format(dtype=dtype.name))
                     dtype = _TD_DTYPE

pandas/tests/dtypes/cast/test_infer_dtype.py

@@ -5,6 +5,7 @@
 
 from pandas.core.dtypes.cast import (
     cast_scalar_to_array,
+    maybe_cast_to_datetime,
     infer_dtype_from_array,
     infer_dtype_from_scalar,
 )
@@ -169,3 +170,14 @@ def test_cast_scalar_to_array(obj, dtype):
 
     arr = cast_scalar_to_array(shape, obj, dtype=dtype)
     tm.assert_numpy_array_equal(arr, exp)
+
+
+@pytest.mark.parametrize(
+    "obj,dtype",
+    [
+        (np.datetime64("2017-01-01 01:00:00"), "datetime64[D]"),
+        (np.datetime64("2017-01-01 02:00:00"), "datetime64[D]"),
+    ],
+)
+def test_maybe_cast_to_datetime(obj, dtype):
+    maybe_cast_to_datetime(obj, dtype)