BUG: Timestamp retains frequency of input Timestamps (pandas-dev#23503)

Author: mroeschke

doc/source/whatsnew/v0.24.0.txt

@@ -1121,6 +1121,7 @@ Datetimelike
 - Bug in :func:`date_range` with frequency of ``Day`` or higher where dates sufficiently far in the future could wrap around to the past instead of raising ``OutOfBoundsDatetime`` (:issue:`14187`)
 - Bug in :class:`PeriodIndex` with attribute ``freq.n`` greater than 1 where adding a :class:`DateOffset` object would return incorrect results (:issue:`23215`)
 - Bug in :class:`Series` that interpreted string indices as lists of characters when setting datetimelike values (:issue:`23451`)
+- Bug in :class:`Timestamp` constructor which would drop the frequency of an input :class:`Timestamp` (:issue:`22311`)
 
 Timedelta
 ^^^^^^^^^

pandas/_libs/tslibs/timestamps.pyx

@@ -16,7 +16,8 @@ from cpython.datetime cimport (datetime,
 PyDateTime_IMPORT
 
 from util cimport (is_datetime64_object, is_timedelta64_object,
-                   is_integer_object, is_string_object, is_array)
+                   is_integer_object, is_string_object, is_array,
+                   is_offset_object)
 
 cimport ccalendar
 from conversion import tz_localize_to_utc, normalize_i8_timestamps
@@ -734,6 +735,9 @@ class Timestamp(_Timestamp):
 
         if is_string_object(freq):
             freq = to_offset(freq)
+        elif not is_offset_object(freq):
+            # GH 22311: Try to extract the frequency of a given Timestamp input
+            freq = getattr(ts_input, 'freq', None)
 
         return create_timestamp_from_ts(ts.value, ts.dts, ts.tzinfo, freq)
 

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -569,6 +569,12 @@ def test_construct_with_different_string_format(self, arg):
         expected = Timestamp(datetime(2013, 1, 1), tz=pytz.FixedOffset(540))
         assert result == expected
 
+    def test_construct_timestamp_preserve_original_frequency(self):
+        # GH 22311
+        result = Timestamp(Timestamp('2010-08-08', freq='D')).freq
+        expected = offsets.Day()
+        assert result == expected
+
 
 class TestTimestamp(object):