TST, MAINT: Add missing components to PR

doc/source/timeseries.rst

@@ -1092,9 +1092,9 @@ frequencies. We will refer to these aliases as *offset aliases*
     "BQ", "business quarter endfrequency"
     "QS", "quarter start frequency"
     "BQS", "business quarter start frequency"
-    "A", "year end frequency"
+    "A, Y", "year end frequency"
     "BA", "business year end frequency"
-    "AS", "year start frequency"
+    "AS, YS", "year start frequency"
     "BAS", "business year start frequency"
     "BH", "business hour frequency"
     "H", "hourly frequency"

doc/source/whatsnew/v0.21.0.txt

@@ -40,6 +40,8 @@ Other Enhancements
 - :func:`DataFrame.clip()` and :func:`Series.clip()` have gained an ``inplace`` argument. (:issue:`15388`)
 - :func:`crosstab` has gained a ``margins_name`` parameter to define the name of the row / column that will contain the totals when ``margins=True``. (:issue:`15972`)
 - :func:`DataFrame.select_dtypes` now accepts scalar values for include/exclude as well as list-like. (:issue:`16855`)
+- :func:`date_range` now accepts 'YS' in addition to 'AS' as an alias for start of year (:issue:`9313`)
+- :func:`date_range` now accepts 'Y' in addition to 'A' as an alias for end of year (:issue:`9313`)
 
 .. _whatsnew_0210.api_breaking:
 

pandas/tests/indexes/datetimes/test_date_range.py

@@ -33,6 +33,30 @@ def test_date_range_gen_error(self):
         rng = date_range('1/1/2000 00:00', '1/1/2000 00:18', freq='5min')
         assert len(rng) == 4
 
+    @pytest.mark.parametrize("freq", ["AS", "YS"])
+    def test_begin_year_alias(self, freq):
+        # see gh-9313
+        rng = date_range("1/1/2013", "7/1/2017", freq=freq)
+        exp = pd.DatetimeIndex(["2013-01-01", "2014-01-01",
+                                "2015-01-01", "2016-01-01"], freq=freq)
+        tm.assert_index_equal(rng, exp)
+
+    @pytest.mark.parametrize("freq", ["A", "Y"])
+    def test_end_year_alias(self, freq):
+        # see gh-9313
+        rng = date_range("1/1/2013", "7/1/2017", freq=freq)
+        exp = pd.DatetimeIndex(["2013-12-31", "2014-12-31",
+                                "2015-12-31", "2016-12-31"], freq=freq)
+        tm.assert_index_equal(rng, exp)
+
+    @pytest.mark.parametrize("freq", ["BA", "BY"])
+    def test_business_end_year_alias(self, freq):
+        # see gh-9313
+        rng = date_range("1/1/2013", "7/1/2017", freq=freq)
+        exp = pd.DatetimeIndex(["2013-12-31", "2014-12-31",
+                                "2015-12-31", "2016-12-30"], freq=freq)
+        tm.assert_index_equal(rng, exp)
+
     def test_date_range_negative_freq(self):
         # GH 11018
         rng = date_range('2011-12-31', freq='-2A', periods=3)

pandas/tseries/frequencies.py

@@ -399,10 +399,14 @@ def _get_freq_str(base, mult=1):
     'Q': 'Q',
     'A': 'A',
     'W': 'W',
-    'M': 'M'
+    'M': 'M',
+    'Y': 'A',
+    'BY': 'A',
+    'YS': 'A',
+    'BYS': 'A',
 }
 
-need_suffix = ['QS', 'BQ', 'BQS', 'AS', 'BA', 'BAS']
+need_suffix = ['QS', 'BQ', 'BQS', 'YS', 'AS', 'BY', 'BA', 'BYS', 'BAS']
 for __prefix in need_suffix:
     for _m in tslib._MONTHS:
         _offset_to_period_map['%s-%s' % (__prefix, _m)] = \
@@ -422,35 +426,18 @@ def get_period_alias(offset_str):
     return _offset_to_period_map.get(offset_str, None)
 
 
-_pure_alias = {
-    # 'A' is equivalent to 'Y'.
-    'Y': 'A',
-    'YS': 'AS',
-    'BY': 'BA',
-    'BYS': 'BAS',
-    'Y-DEC': 'A-DEC',
-    'Y-JAN': 'A-JAN',
-    'Y-FEB': 'A-FEB',
-    'Y-MAR': 'A-MAR',
-    'Y-APR': 'A-APR',
-    'Y-MAY': 'A-MAY',
-    'Y-JUN': 'A-JUN',
-    'Y-JUL': 'A-JUL',
-    'Y-AUG': 'A-AUG',
-    'Y-SEP': 'A-SEP',
-    'Y-OCT': 'A-OCT',
-    'Y-NOV': 'A-NOV',
-}
-
-
 _lite_rule_alias = {
     'W': 'W-SUN',
     'Q': 'Q-DEC',
 
     'A': 'A-DEC',  # YearEnd(month=12),
+    'Y': 'A-DEC',
     'AS': 'AS-JAN',  # YearBegin(month=1),
+    'YS': 'AS-JAN',
     'BA': 'BA-DEC',  # BYearEnd(month=12),
+    'BY': 'BA-DEC',
     'BAS': 'BAS-JAN',  # BYearBegin(month=1),
+    'BYS': 'BAS-JAN',
 
     'Min': 'T',
     'min': 'T',
@@ -730,16 +717,26 @@ def get_standard_freq(freq):
     _reverse_period_code_map[_v] = _k
 
 # Additional aliases
+year_aliases = {}
+
+for k, v in compat.iteritems(_period_code_map):
+    if k.startswith("A-"):
+        alias = "Y" + k[1:]
+        year_aliases[alias] = v
+
+_period_code_map.update(**year_aliases)
+del year_aliases
+
 _period_code_map.update({
     "Q": 2000,  # Quarterly - December year end (default quarterly)
     "A": 1000,  # Annual
+    "Y": 1000,
     "W": 4000,  # Weekly
     "C": 5000,  # Custom Business Day
 })
 
 
 def _period_str_to_code(freqstr):
-    freqstr = _pure_alias.get(freqstr, freqstr)
     freqstr = _lite_rule_alias.get(freqstr, freqstr)
 
     if freqstr not in _dont_uppercase: