BUG: Return local Timestamp.weekday_name attribute (pandas-dev#17354) (pandas-dev#17377)

Author: mroeschke

doc/source/whatsnew/v0.21.0.txt

@@ -399,6 +399,7 @@ Conversion
 - Fixed the return type of ``IntervalIndex.is_non_overlapping_monotonic`` to be a Python ``bool`` for consistency with similar attributes/methods.  Previously returned a ``numpy.bool_``. (:issue:`17237`)
 - Bug in ``IntervalIndex.is_non_overlapping_monotonic`` when intervals are closed on both sides and overlap at a point (:issue:`16560`)
 - Bug in :func:`Series.fillna` returns frame when ``inplace=True`` and ``value`` is dict (:issue:`16156`)
+- Bug in :attr:`Timestamp.weekday_name` returning a UTC-based weekday name when localized to a timezone (:issue:`17354`)
 
 Indexing
 ^^^^^^^^

pandas/_libs/tslib.pyx

@@ -534,9 +534,7 @@ class Timestamp(_Timestamp):
 
     @property
     def weekday_name(self):
-        out = get_date_name_field(
-            np.array([self.value], dtype=np.int64), 'weekday_name')
-        return out[0]
+        return self._get_named_field('weekday_name')
 
     @property
     def dayofyear(self):
@@ -1271,13 +1269,29 @@ cdef class _Timestamp(datetime):
         # same timezone if specified)
         return datetime.__sub__(self, other)
 
-    cpdef _get_field(self, field):
+    cdef int64_t _maybe_convert_value_to_local(self):
+        """Convert UTC i8 value to local i8 value if tz exists"""
+        cdef:
+            int64_t val
         val = self.value
         if self.tz is not None and not _is_utc(self.tz):
             val = tz_convert_single(self.value, 'UTC', self.tz)
+        return val
+
+    cpdef _get_field(self, field):
+        cdef:
+            int64_t val
+        val = self._maybe_convert_value_to_local()
         out = get_date_field(np.array([val], dtype=np.int64), field)
         return int(out[0])
 
+    cpdef _get_named_field(self, field):
+        cdef:
+            int64_t val
+        val = self._maybe_convert_value_to_local()
+        out = get_date_name_field(np.array([val], dtype=np.int64), field)
+        return out[0]
+
     cpdef _get_start_end_field(self, field):
         month_kw = self.freq.kwds.get(
             'startingMonth', self.freq.kwds.get(

pandas/tests/scalar/test_timestamp.py

@@ -555,6 +555,14 @@ def check(value, equal):
         for end in ends:
             assert getattr(ts, end)
 
+    @pytest.mark.parametrize('data, expected',
+                             [(Timestamp('2017-08-28 23:00:00'), 'Monday'),
+                              (Timestamp('2017-08-28 23:00:00', tz='EST'),
+                               'Monday')])
+    def test_weekday_name(self, data, expected):
+        # GH 17354
+        assert data.weekday_name == expected
+
     def test_pprint(self):
         # GH12622
         import pprint