BUG: Bug in to_datetime with a format and coerce=True not raising (GH5195)

doc/source/release.rst

@@ -593,6 +593,7 @@ Bug Fixes
   - Compound dtypes in a constructor raise ``NotImplementedError`` (:issue:`5191`)
   - Bug in comparing duplicate frames (:issue:`4421`) related
   - Bug in describe on duplicate frames
+  - Bug in ``to_datetime`` with a format and ``coerce=True`` not raising (:issue:`5195`)
 
 pandas 0.12.0
 -------------

pandas/tseries/tests/test_timeseries.py

@@ -879,6 +879,29 @@ def test_to_datetime_on_datetime64_series(self):
         result = to_datetime(s)
         self.assertEquals(result[0], s[0])
 
+    def test_to_datetime_with_apply(self):
+
+        # this is only locale tested with US/None locales
+        import locale
+        (lang,encoding) = locale.getlocale()
+        if lang is not None:
+            raise nose.SkipTest("format codes cannot work with a locale of {0}".format(lang))
+
+        # GH 5195
+        # with a format and coerce a single item to_datetime fails
+        td = Series(['May 04', 'Jun 02', 'Dec 11'], index=[1,2,3])
+        expected = pd.to_datetime(td, format='%b %y')
+        result = td.apply(pd.to_datetime, format='%b %y')
+        assert_series_equal(result, expected)
+
+        td = pd.Series(['May 04', 'Jun 02', ''], index=[1,2,3])
+        self.assertRaises(ValueError, lambda : pd.to_datetime(td,format='%b %y'))
+        self.assertRaises(ValueError, lambda : td.apply(pd.to_datetime, format='%b %y'))
+        expected = pd.to_datetime(td, format='%b %y', coerce=True)
+
+        result = td.apply(lambda x: pd.to_datetime(x, format='%b %y', coerce=True))
+        assert_series_equal(result, expected)
+
     def test_nat_vector_field_access(self):
         idx = DatetimeIndex(['1/1/2000', None, None, '1/4/2000'])
 

pandas/tseries/tools.py

@@ -112,7 +112,7 @@ def _convert_listlike(arg, box):
 
                 # fallback
                 if result is None:
-                    result = tslib.array_strptime(arg, format)
+                    result = tslib.array_strptime(arg, format, coerce=coerce)
             else:
                 result = tslib.array_to_datetime(arg, raise_=errors == 'raise',
                                                  utc=utc, dayfirst=dayfirst,

pandas/tslib.pyx

@@ -1174,7 +1174,7 @@ def repr_timedelta64(object value):
 
    return "%s%02d:%02d:%s" % (sign_pretty, hours, minutes, seconds_pretty)
 
-def array_strptime(ndarray[object] values, object fmt):
+def array_strptime(ndarray[object] values, object fmt, coerce=False):
     cdef:
         Py_ssize_t i, n = len(values)
         pandas_datetimestruct dts
@@ -1237,9 +1237,15 @@ def array_strptime(ndarray[object] values, object fmt):
     for i in range(n):
         found = format_regex.match(values[i])
         if not found:
+            if coerce:
+                iresult[i] = iNaT
+                continue
             raise ValueError("time data %r does not match format %r" %
                              (values[i], fmt))
         if len(values[i]) != found.end():
+            if coerce:
+                iresult[i] = iNaT
+                continue
             raise ValueError("unconverted data remains: %s" %
                               values[i][found.end():])
         year = 1900