ENH: support .strftime for datetimelikes (closes #10086)

Author: mortada

pandas/tests/test_series.py

@@ -81,9 +81,10 @@ def test_dt_namespace_accessor(self):
 
         ok_for_base = ['year','month','day','hour','minute','second','weekofyear','week','dayofweek','weekday','dayofyear','quarter','freq','days_in_month','daysinmonth']
         ok_for_period = ok_for_base + ['qyear']
+        ok_for_period_methods = ['strftime']
         ok_for_dt = ok_for_base + ['date','time','microsecond','nanosecond', 'is_month_start', 'is_month_end', 'is_quarter_start',
                                    'is_quarter_end', 'is_year_start', 'is_year_end', 'tz']
-        ok_for_dt_methods = ['to_period','to_pydatetime','tz_localize','tz_convert', 'normalize']
+        ok_for_dt_methods = ['to_period','to_pydatetime','tz_localize','tz_convert', 'normalize', 'strftime']
         ok_for_td = ['days','seconds','microseconds','nanoseconds']
         ok_for_td_methods = ['components','to_pytimedelta']
 
@@ -109,13 +110,12 @@ def compare(s, name):
                   Series(date_range('20130101',periods=5,freq='s')),
                   Series(date_range('20130101 00:00:00',periods=5,freq='ms'))]:
             for prop in ok_for_dt:
-
                 # we test freq below
                 if prop != 'freq':
                     compare(s, prop)
 
             for prop in ok_for_dt_methods:
-                getattr(s.dt,prop)
+                getattr(s.dt, prop)
 
             result = s.dt.to_pydatetime()
             self.assertIsInstance(result,np.ndarray)
@@ -140,13 +140,12 @@ def compare(s, name):
                   Series(timedelta_range('1 day 01:23:45',periods=5,freq='s')),
                   Series(timedelta_range('2 days 01:23:45.012345',periods=5,freq='ms'))]:
             for prop in ok_for_td:
-
                 # we test freq below
                 if prop != 'freq':
                     compare(s, prop)
 
             for prop in ok_for_td_methods:
-                getattr(s.dt,prop)
+                getattr(s.dt, prop)
 
             result = s.dt.components
             self.assertIsInstance(result,DataFrame)
@@ -169,13 +168,14 @@ def compare(s, name):
 
         # periodindex
         for s in [Series(period_range('20130101',periods=5,freq='D'))]:
-
             for prop in ok_for_period:
-
                 # we test freq below
                 if prop != 'freq':
                     compare(s, prop)
 
+            for prop in ok_for_period_methods:
+                getattr(s.dt, prop)
+
             freq_result = s.dt.freq
             self.assertEqual(freq_result, PeriodIndex(s.values).freq)
 
@@ -190,7 +190,7 @@ def get_dir(s):
 
         s = Series(period_range('20130101',periods=5,freq='D').asobject)
         results = get_dir(s)
-        tm.assert_almost_equal(results,list(sorted(set(ok_for_period))))
+        tm.assert_almost_equal(results, list(sorted(set(ok_for_period + ok_for_period_methods))))
 
         # no setting allowed
         s = Series(date_range('20130101',periods=5,freq='D'))
@@ -203,6 +203,27 @@ def f():
                 s.dt.hour[0] = 5
             self.assertRaises(com.SettingWithCopyError, f)
 
+    def test_strftime(self):
+        # GH 10086
+        s = Series(date_range('20130101', periods=5))
+        result = s.dt.strftime('%Y/%m/%d')
+        expected = Series(['2013/01/01', '2013/01/02', '2013/01/03', '2013/01/04', '2013/01/05'])
+        tm.assert_series_equal(result, expected)
+
+        s.iloc[0] = pd.NaT
+        result = s.dt.strftime('%Y/%m/%d')
+        expected = Series(['NaT', '2013/01/02', '2013/01/03', '2013/01/04', '2013/01/05'])
+        tm.assert_series_equal(result, expected)
+
+        datetime_index = date_range('20150301', periods=5)
+        result = datetime_index.strftime("%Y/%m/%d")
+        expected = ['2015/03/01', '2015/03/02', '2015/03/03', '2015/03/04', '2015/03/05']
+        self.assertEqual(result, expected)
+
+        period_index = period_range('20150301', periods=5)
+        expected = ['2015/03/01', '2015/03/02', '2015/03/03', '2015/03/04', '2015/03/05']
+        self.assertEqual(result, expected)
+
     def test_valid_dt_with_missing_values(self):
 
         from datetime import date, time

pandas/tseries/common.py

@@ -125,7 +125,7 @@ def to_pydatetime(self):
                                            accessors=DatetimeIndex._datetimelike_ops,
                                            typ='property')
 DatetimeProperties._add_delegate_accessors(delegate=DatetimeIndex,
-                                           accessors=["to_period","tz_localize","tz_convert","normalize"],
+                                           accessors=["to_period","tz_localize","tz_convert","normalize","strftime"],
                                            typ='method')
 
 class TimedeltaProperties(Properties):
@@ -181,6 +181,9 @@ class PeriodProperties(Properties):
 PeriodProperties._add_delegate_accessors(delegate=PeriodIndex,
                                          accessors=PeriodIndex._datetimelike_ops,
                                          typ='property')
+PeriodProperties._add_delegate_accessors(delegate=PeriodIndex,
+                                         accessors=["strftime"],
+                                         typ='method')
 
 
 class CombinedDatetimelikeProperties(DatetimeProperties, TimedeltaProperties):

pandas/tseries/index.py

@@ -694,6 +694,21 @@ def astype(self, dtype):
         else:  # pragma: no cover
             raise ValueError('Cannot cast DatetimeIndex to dtype %s' % dtype)
 
+    def strftime(self, date_format):
+        """
+        Return a list of formmatted strings specified by date_format
+
+        Parameters
+        ----------
+        date_format : str
+            date format string (e.g. "%Y-%m-%d")
+
+        Returns
+        -------
+        a list formatted strings
+        """
+        return self.format(date_format=date_format)
+
     def _get_time_micros(self):
         utc = _utc()
         values = self.asi8

pandas/tseries/period.py

@@ -328,6 +328,21 @@ def astype(self, dtype):
             return Index(self.values, dtype)
         raise ValueError('Cannot cast PeriodIndex to dtype %s' % dtype)
 
+    def strftime(self, date_format):
+        """
+        Return a list of formmatted strings specified by date_format
+
+        Parameters
+        ----------
+        date_format : str
+            date format string (e.g. "%Y-%m-%d")
+
+        Returns
+        -------
+        a list formatted strings
+        """
+        return self.format(date_format=date_format)
+
     def searchsorted(self, key, side='left'):
         if isinstance(key, Period):
             if key.freq != self.freq: