one more

Author: jbrockmendel

pandas/core/dtypes/cast.py

@@ -1195,9 +1195,7 @@ def maybe_cast_to_datetime(
 
     # TODO: _from_sequence would raise ValueError in cases where
     #  _ensure_nanosecond_dtype raises TypeError
-    # Incompatible types in assignment (expression has type "Union[dtype[Any],
-    # ExtensionDtype]", variable has type "Optional[dtype[Any]]")
-    dtype = _ensure_nanosecond_dtype(dtype)  # type: ignore[assignment]
+    _ensure_nanosecond_dtype(dtype)
 
     if is_timedelta64_dtype(dtype):
         res = TimedeltaArray._from_sequence(value, dtype=dtype)
@@ -1235,12 +1233,11 @@ def sanitize_to_nanoseconds(values: np.ndarray, copy: bool = False) -> np.ndarra
     return values
 
 
-def _ensure_nanosecond_dtype(dtype: DtypeObj) -> DtypeObj:
+def _ensure_nanosecond_dtype(dtype: DtypeObj) -> None:
     """
     Convert dtypes with granularity less than nanosecond to nanosecond
 
     >>> _ensure_nanosecond_dtype(np.dtype("M8[us]"))
-    dtype('<M8[us]')
 
     >>> _ensure_nanosecond_dtype(np.dtype("M8[D]"))
     Traceback (most recent call last):
@@ -1277,7 +1274,6 @@ def _ensure_nanosecond_dtype(dtype: DtypeObj) -> DtypeObj:
                 f"dtype={dtype} is not supported. Supported resolutions are 's', "
                 "'ms', 'us', and 'ns'"
             )
-    return dtype
 
 
 # TODO: other value-dependent functions to standardize here include