PERF: add shortcut to Timedelta constructor

asv_bench/benchmarks/tslibs/timedelta.py

@@ -10,6 +10,11 @@
 
 
 class TimedeltaConstructor:
+    def setup(self):
+        self.nptimedelta64 = np.timedelta64(3600)
+        self.dttimedelta = datetime.timedelta(seconds=3600)
+        self.td = Timedelta(3600, unit="s")
+
     def time_from_int(self):
         Timedelta(123456789)
 
@@ -28,10 +33,10 @@ def time_from_components(self):
         )
 
     def time_from_datetime_timedelta(self):
-        Timedelta(datetime.timedelta(days=1, seconds=1))
+        Timedelta(self.dttimedelta)
 
     def time_from_np_timedelta(self):
-        Timedelta(np.timedelta64(1, "ms"))
+        Timedelta(self.nptimedelta64)
 
     def time_from_string(self):
         Timedelta("1 days")
@@ -42,6 +47,9 @@ def time_from_iso_format(self):
     def time_from_missing(self):
         Timedelta("nat")
 
+    def time_from_pd_timedelta(self):
+        TimeDelta(self.td)
+
 
 class TimedeltaProperties:
     def setup_cache(self):

doc/source/whatsnew/v1.1.0.rst

@@ -72,7 +72,7 @@ Deprecations
 
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
-
+- Performance improvement in :class:`Timedelta` constructor (:issue:`30543`)
 -
 -
 

pandas/_libs/tslibs/timedeltas.pyx

@@ -1208,7 +1208,12 @@ class Timedelta(_Timedelta):
                 "represent unambiguous timedelta values durations."
             )
 
-        if isinstance(value, Timedelta):
+        # GH 30543 if pd.Timedelta already passed, return it
+        # check that only value is passed
+        if (isinstance(value, Timedelta) and unit is None and
+                len(kwargs) == 0):
+            return value
+        elif isinstance(value, Timedelta):
             value = value.value
         elif isinstance(value, str):
             if len(value) > 0 and value[0] == 'P':

pandas/tests/indexes/datetimes/test_constructors.py

@@ -950,3 +950,10 @@ def test_datetimeindex_constructor_misc(self):
         )
         assert len(idx1) == len(idx2)
         assert idx1.freq == idx2.freq
+
+
+def test_timedelta_constructor_identity():
+    # Test for #30543
+    expected = pd.Timedelta(np.timedelta64(1, "s"))
+    result = pd.Timedelta(expected)
+    assert result is expected