ENH: Support day_of_year over dayofyear (pandas-dev#9606)

Similar to changes for day_of_week, create aliases for day_of_year and add to respective test files to ensure back-compat.
Also fix whatsnew rst file

Author: abhishekmangla

doc/source/whatsnew/v1.2.0.rst

@@ -15,18 +15,11 @@ Enhancements
 
 .. _whatsnew_120.improve_timeseries_accessor_naming:
 Improve Timeseries accessors Naming Convention
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-In modules like Period, PeriodArray, and Timestamp, there are non-Pythonic property names ``dayofweek`` and ``dayofyear`` (:issue:`9606`). We continue to maintain backwards-compatibility by simply aliasing the old naming convention to the new, properly named functions ``day_of_week`` and ``day_of_year``.
-
-For example:
-
-.. ipython:: python
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-   import pandas as pd
+- Added ``day_of_week`` (compatibility alias ``dayofweek``) property to ``Timestamp``, ``DatetimeIndex``, ``Period``, ``PeriodIndex`` (:issue:`9605`)
 
-   per = pd.Period('2017-12-31 22:00', 'H')
-   per.dayofweek == per.day_of_week == 6
+- Added ``day_of_year`` (compatibility alias ``dayofyear``) property to ``Timestamp``, ``DatetimeIndex``, ``Period``, ``PeriodIndex`` (:issue:`9605`)
 
 .. _whatsnew_120.duplicate_labels:
 

pandas/_libs/tslibs/nattype.pyx

@@ -357,6 +357,7 @@ class NaTType(_NaT):
 
     week = property(fget=lambda self: np.nan)
     dayofyear = property(fget=lambda self: np.nan)
+    day_of_year = property(fget=lambda self: np.nan)
     weekofyear = property(fget=lambda self: np.nan)
     days_in_month = property(fget=lambda self: np.nan)
     daysinmonth = property(fget=lambda self: np.nan)

pandas/_libs/tslibs/period.pyx

@@ -1475,8 +1475,8 @@ cdef class _Period(PeriodMixin):
         PeriodDtypeBase _dtype
         BaseOffset freq
 
-    # Alias dayofweek function to day_of_week (GH-9606)
     dayofweek = _Period.day_of_week
+    dayofyear = _Period.day_of_year
 
     def __cinit__(self, int64_t ordinal, BaseOffset freq):
         self.ordinal = ordinal
@@ -1989,7 +1989,7 @@ cdef class _Period(PeriodMixin):
         return self.dayofweek
 
     @property
-    def dayofyear(self) -> int:
+    def day_of_year(self) -> int:
         """
         Return the day of the year.
 
@@ -2005,19 +2005,19 @@ cdef class _Period(PeriodMixin):
         See Also
         --------
         Period.day : Return the day of the month.
-        Period.dayofweek : Return the day of week.
-        PeriodIndex.dayofyear : Return the day of year of all indexes.
+        Period.day_of_week : Return the day of week.
+        PeriodIndex.day_of_year : Return the day of year of all indexes.
 
         Examples
         --------
         >>> period = pd.Period("2015-10-23", freq='H')
-        >>> period.dayofyear
+        >>> period.day_of_year
         296
         >>> period = pd.Period("2012-12-31", freq='D')
-        >>> period.dayofyear
+        >>> period.day_of_year
         366
         >>> period = pd.Period("2013-01-01", freq='D')
-        >>> period.dayofyear
+        >>> period.day_of_year
         1
         """
         base = self._dtype._dtype_code

pandas/_libs/tslibs/timestamps.pyx

@@ -230,8 +230,8 @@ cdef class _Timestamp(ABCTimestamp):
 
     # higher than np.ndarray and np.matrix
     __array_priority__ = 100
-    # Alias dayofweek function to day_of_week (GH-9606)
     dayofweek = _Timestamp.day_of_week
+    dayofyear = _Timestamp.day_of_year
 
     def __hash__(_Timestamp self):
         if self.nanosecond:
@@ -547,7 +547,7 @@ cdef class _Timestamp(ABCTimestamp):
         return self.weekday()
 
     @property
-    def dayofyear(self) -> int:
+    def day_of_year(self) -> int:
         """
         Return the day of the year.
         """

pandas/core/arrays/datetimes.py

@@ -179,6 +179,7 @@ class DatetimeArray(dtl.TimelikeOps, dtl.DatelikeOps):
         "dayofweek",
         "day_of_week",
         "dayofyear",
+        "day_of_year",
         "quarter",
         "days_in_month",
         "daysinmonth",
@@ -1538,13 +1539,14 @@ def weekofyear(self):
     dayofweek = day_of_week
     weekday = day_of_week
 
-    dayofyear = _field_accessor(
+    day_of_year = _field_accessor(
         "dayofyear",
         "doy",
         """
         The ordinal day of the year.
         """,
     )
+    dayofyear = day_of_year
     quarter = _field_accessor(
         "quarter",
         "q",

pandas/core/arrays/period.py

@@ -142,6 +142,7 @@ class PeriodArray(PeriodMixin, dtl.DatelikeOps):
         "dayofweek",
         "day_of_week",
         "dayofyear",
+        "day_of_year",
         "quarter",
         "qyear",
         "days_in_month",

pandas/core/indexes/datetimes.py

@@ -158,6 +158,7 @@ class DatetimeIndex(DatetimeTimedeltaMixin):
     time
     timetz
     dayofyear
+    day_of_year
     weekofyear
     week
     dayofweek

pandas/core/indexes/period.py

@@ -97,6 +97,7 @@ class PeriodIndex(DatetimeIndexOpsMixin, Int64Index):
     dayofweek
     day_of_week
     dayofyear
+    day_of_year
     days_in_month
     daysinmonth
     end_time

pandas/tests/generic/test_finalize.py

@@ -680,6 +680,7 @@ def test_datetime_method(method):
         "dayofweek",
         "day_of_week",
         "dayofyear",
+        "day_of_year",
         "quarter",
         "is_month_start",
         "is_month_end",

pandas/tests/indexes/datetimes/test_scalar_compat.py

@@ -40,6 +40,7 @@ def test_dti_date_out_of_range(self, data):
             "dayofweek",
             "day_of_week",
             "dayofyear",
+            "day_of_year",
             "quarter",
             "days_in_month",
             "is_month_start",

pandas/tests/indexes/period/test_period.py

@@ -251,6 +251,7 @@ def _check_all_fields(self, periodindex):
             "dayofweek",
             "day_of_week",
             "dayofyear",
+            "day_of_year",
             "quarter",
             "qyear",
             "days_in_month",

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -66,6 +66,7 @@ def check(value, equal):
         check(ts.day_of_week, 6)
         check(ts.quarter, 2)
         check(ts.dayofyear, 130)
+        check(ts.day_of_year, 130)
         check(ts.week, 19)
         check(ts.daysinmonth, 31)
         check(ts.daysinmonth, 31)
@@ -87,6 +88,7 @@ def check(value, equal):
         check(ts.day_of_week, 2)
         check(ts.quarter, 4)
         check(ts.dayofyear, 365)
+        check(ts.day_of_year, 365)
         check(ts.week, 1)
         check(ts.daysinmonth, 31)