BUG: datetime64 formatting issues in DataFrame.to_csv. close #1993

RELEASE.rst

@@ -242,6 +242,7 @@ pandas 0.9.0
     (#1970)
   - Fix reset_index bug if both drop and level are specified (#1957)
   - Work around unsafe NumPy object->int casting with Cython function (#1987)
+  - Fix datetime64 formatting bug in DataFrame.to_csv (#1993)
 
 
 pandas 0.8.1

pandas/core/frame.py

@@ -1106,8 +1106,11 @@ def _helper_csvexcel(self, writer, na_rep=None, cols=None,
                 val = series[col][j]
                 if lib.checknull(val):
                     val = na_rep
+
                 if float_format is not None and com.is_float(val):
                     val = float_format % val
+                elif isinstance(val, np.datetime64):
+                    val = lib.Timestamp(val)._repr_base
 
                 row_fields.append(val)
 
@@ -4391,7 +4394,7 @@ def var(self, axis=0, skipna=True, level=None, ddof=1):
 
     @Substitution(name='standard deviation', shortname='std',
                   na_action=_doc_exclude_na, extras='')
-    @Appender(_stat_doc + 
+    @Appender(_stat_doc +
         """
         Normalized by N-1 (unbiased estimator).
         """)

pandas/tseries/tests/test_timeseries.py

@@ -23,6 +23,8 @@
 from pandas.util.testing import assert_series_equal, assert_almost_equal
 import pandas.util.testing as tm
 
+from pandas.util.py3compat import StringIO
+
 from pandas.lib import NaT, iNaT
 import pandas.lib as lib
 import cPickle as pickle
@@ -1185,6 +1187,14 @@ def test_to_html_timestamp(self):
         result = df.to_html()
         self.assert_('2000-01-01' in result)
 
+    def test_to_csv_numpy_16_bug(self):
+        frame = DataFrame({'a': date_range('1/1/2000', periods=10)})
+
+        buf = StringIO()
+        frame.to_csv(buf)
+
+        result = buf.getvalue()
+        self.assert_('2000-01-01' in result)
 
 def _simple_ts(start, end, freq='D'):
     rng = date_range(start, end, freq=freq)