API: use ISO8601 format for Period repr, close #1776

RELEASE.rst

@@ -52,6 +52,7 @@ pandas 0.9.0
   - The internal HDF5 data arrangement for DataFrames has been
     transposed. Legacy files will still be readable by HDFStore (#1834, #1824)
   - Legacy cruft removed: pandas.stats.misc.quantileTS
+  - Use ISO8601 format for Period repr: monthly, daily, and on down (#1776)
 
 **Bug fixes**
 

pandas/src/plib.pyx

@@ -230,21 +230,21 @@ def period_format(int64_t value, int freq, object fmt=None):
         elif freq_group == 2000: # FR_QTR
             fmt = b'%FQ%q'
         elif freq_group == 3000: # FR_MTH
-            fmt = b'%b-%Y'
+            fmt = b'%Y-%m'
         elif freq_group == 4000: # WK
             left = period_asfreq(value, freq, 6000, 0)
             right = period_asfreq(value, freq, 6000, 1)
             return '%s/%s' % (period_format(left, 6000),
                               period_format(right, 6000))
         elif (freq_group == 5000 # BUS
               or freq_group == 6000): # DAY
-            fmt = b'%d-%b-%Y'
+            fmt = b'%Y-%m-%d'
         elif freq_group == 7000: # HR
-            fmt = b'%d-%b-%Y %H:00'
+            fmt = b'%Y-%m-%d %H:00'
         elif freq_group == 8000: # MIN
-            fmt = b'%d-%b-%Y %H:%M'
+            fmt = b'%Y-%m-%d %H:%M'
         elif freq_group == 9000: # SEC
-            fmt = b'%d-%b-%Y %H:%M:%S'
+            fmt = b'%Y-%m-%d %H:%M:%S'
         else:
             raise ValueError('Unknown freq: %d' % freq)
 

pandas/tseries/tests/test_period.py

@@ -192,7 +192,10 @@ def test_freq_str(self):
 
     def test_repr(self):
         p = Period('Jan-2000')
-        self.assert_('Jan-2000' in repr(p))
+        self.assert_('2000-01' in repr(p))
+
+        p = Period('2000-12-15')
+        self.assert_('2000-12-15' in repr(p))
 
     def test_strftime(self):
         p = Period('2000-1-1 12:34:12', freq='S')