Performance of maybe_box_datetimelike #30520

pandas/core/common.py

@@ -72,7 +72,6 @@ def consensus_name_attr(objs):
 
 
 def maybe_box(indexer, values, obj, key):
-
     # if we have multiples coming back, box em
     if isinstance(values, np.ndarray):
         return obj[indexer.get_loc(key)]
@@ -84,9 +83,13 @@ def maybe_box(indexer, values, obj, key):
 def maybe_box_datetimelike(value):
     # turn a datetime like into a Timestamp/timedelta as needed
 
-    if isinstance(value, (np.datetime64, datetime)):
+    if isinstance(value, (np.datetime64, datetime)) and (
+            not isinstance(value, tslibs.Timestamp)) and (
+            notnull(value)):
         value = tslibs.Timestamp(value)
-    elif isinstance(value, (np.timedelta64, timedelta)):
+    elif isinstance(value, (np.timedelta64, timedelta)) and (
+            not isinstance(value, tslibs.Timedelta)) and (
+            notnull(value)):
         value = tslibs.Timedelta(value)
 
     return value
@@ -119,7 +122,7 @@ def is_bool_indexer(key: Any) -> bool:
     """
     na_msg = "cannot index with vector containing NA / NaN values"
     if isinstance(key, (ABCSeries, np.ndarray, ABCIndex)) or (
-        is_array_like(key) and is_extension_array_dtype(key.dtype)
+            is_array_like(key) and is_extension_array_dtype(key.dtype)
     ):
         if key.dtype == np.object_:
             key = np.asarray(values_from_object(key))
@@ -215,7 +218,6 @@ def try_sort(iterable):
 
 
 def asarray_tuplesafe(values, dtype=None):
-
     if not (isinstance(values, (list, tuple)) or hasattr(values, "__array__")):
         values = list(values)
     elif isinstance(values, ABCIndexClass):
@@ -284,10 +286,10 @@ def is_null_slice(obj):
     We have a null slice.
     """
     return (
-        isinstance(obj, slice)
-        and obj.start is None
-        and obj.stop is None
-        and obj.step is None
+            isinstance(obj, slice)
+            and obj.start is None
+            and obj.stop is None
+            and obj.step is None
     )
 
 
@@ -304,7 +306,7 @@ def is_full_slice(obj, l):
     We have a full length slice.
     """
     return (
-        isinstance(obj, slice) and obj.start == 0 and obj.stop == l and obj.step is None
+            isinstance(obj, slice) and obj.start == 0 and obj.stop == l and obj.step is None
     )