fix Timestamp.resolution pandas-dev#21336

Author: jbrockmendel

doc/source/whatsnew/v0.24.0.txt

@@ -301,6 +301,7 @@ Datetimelike
 ^^^^^^^^^^^^
 
 - Fixed bug where two :class:`DateOffset` objects with different ``normalize`` attributes could evaluate as equal (:issue:`21404`)
+- Fixed bug where :meth:`Timestamp.resolution` incorrectly returned 1-microsecond ``timedelta`` instead of 1-nanosecond :class:`Timedelta` (:issue:`21336`,:issue:`21365`)
 
 Timedelta
 ^^^^^^^^^

pandas/_libs/tslibs/timestamps.pyx

@@ -407,6 +407,15 @@ cdef class _Timestamp(datetime):
     def asm8(self):
         return np.datetime64(self.value, 'ns')
 
+    @property
+    def resolution(self):
+        """
+        Return resolution describing the smallest difference between two
+        times that can be represented by Timestamp object_state
+        """
+        # GH#21336, GH#21365
+        return Timedelta(nanoseconds=1)
+
     def timestamp(self):
         """Return POSIX timestamp as float."""
         # py27 compat, see GH#17329

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -172,6 +172,11 @@ def test_woy_boundary(self):
                                2005, 1, 1), (2005, 1, 2)]])
         assert (result == [52, 52, 53, 53]).all()
 
+    def test_resolution(self):
+        # GH#21336, GH#21365
+        dt = Timestamp('2100-01-01 00:00:00')
+        assert dt.resolution == Timedelta(nanoseconds=1)
+
 
 class TestTimestampConstructors(object):