BUG: GH19458 fixes precision issue in TimeDelta.total_seconds()

doc/source/whatsnew/v0.23.0.txt

@@ -733,6 +733,7 @@ Datetimelike
 - Bug in :func:`to_datetime` where passing an out-of-bounds datetime with ``errors='coerce'`` and ``utc=True`` would raise ``OutOfBoundsDatetime`` instead of parsing to ``NaT`` (:issue:`19612`)
 - Bug in :func:`Timedelta.__add__`, :func:`Timedelta.__sub__` where adding or subtracting a ``np.timedelta64`` object would return another ``np.timedelta64`` instead of a ``Timedelta`` (:issue:`19738`)
 - Bug in :func:`Timedelta.__floordiv__`, :func:`Timedelta.__rfloordiv__` where operating with a ``Tick`` object would raise a ``TypeError`` instead of returning a numeric value (:issue:`19738`)
+- Bug in :func:`Timedelta.total_seconds()` causing precision errors i.e. `Timedelta('30S').total_seconds()==30.000000000000004` (:issue:`19458`)
 
 
 Timezones

pandas/_libs/tslibs/timedeltas.pyx

@@ -739,7 +739,7 @@ cdef class _Timedelta(timedelta):
         """
         Total duration of timedelta in seconds (to ns precision)
         """
-        return 1e-9 * self.value
+        return self.value / 1e9
 
     def view(self, dtype):
         """ array view compat """

pandas/tests/scalar/timedelta/test_timedelta.py

@@ -512,6 +512,15 @@ def test_implementation_limits(self):
         with pytest.raises(OverflowError):
             Timedelta(max_td.value + 1, 'ns')
 
+    def test_total_seconds_precision(self):
+        # GH 19458
+        assert Timedelta('30S').total_seconds() == 30.0
+        assert Timedelta('0').total_seconds() == 0.0
+        assert Timedelta('-2S').total_seconds() == -2.0
+        assert Timedelta('5.324S').total_seconds() == 5.324
+        assert (Timedelta('30S').total_seconds() - 30.0) < 1e-20
+        assert (30.0 - Timedelta('30S').total_seconds()) < 1e-20
+
     def test_timedelta_arithmetic(self):
         data = pd.Series(['nat', '32 days'], dtype='timedelta64[ns]')
         deltas = [timedelta(days=1), Timedelta(1, unit='D')]