BUG: fix IndexError for invalid integer dates %Y%m%d with errors='ignore' (# GH 26583)

array_strptime returned IndexError when trying to slice 'too long' integer for the given format %Y%m%d. Note, it tried to parse 20209911 to datetime(2020, 9, 9) and having 11 left tried to return it in ValueError message as a slice of integer which in turn caused IndexError. String representation of the value is now used to be able to make slice.

Author: nathalier

pandas/_libs/tslibs/strptime.pyx

@@ -140,13 +140,13 @@ def array_strptime(object[:] values, object fmt,
                     iresult[i] = NPY_NAT
                     continue
                 raise ValueError("time data %r does not match "
-                                 "format %r (match)" % (values[i], fmt))
+                                 "format %r (match)" % (val, fmt))
             if len(val) != found.end():
                 if is_coerce:
                     iresult[i] = NPY_NAT
                     continue
                 raise ValueError("unconverted data remains: %s" %
-                                 values[i][found.end():])
+                                 val[found.end():])
 
         # search
         else:
@@ -156,7 +156,7 @@ def array_strptime(object[:] values, object fmt,
                     iresult[i] = NPY_NAT
                     continue
                 raise ValueError("time data %r does not match format "
-                                 "%r (search)" % (values[i], fmt))
+                                 "%r (search)" % (val, fmt))
 
         iso_year = -1
         year = 1900

pandas/tests/indexes/datetimes/test_tools.py

@@ -114,6 +114,17 @@ def test_to_datetime_format_integer(self, cache):
         result = to_datetime(s, format='%Y%m', cache=cache)
         assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize('int_date, expected', [
+        [20121030, datetime(2012, 10, 30)],
+        [20129930, 20129930],
+        [20120011, 20120011],
+        [2012010101, 2012010101]])
+    def test_int_to_datetime_format_YYYYMMDD_indexerror(self, int_date,
+                                                        expected):
+        # GH 26583
+        result = to_datetime(int_date, format='%Y%m%d', errors='ignore')
+        assert result == expected
+
     @pytest.mark.parametrize('cache', [True, False])
     def test_to_datetime_format_microsecond(self, cache):