BUG: fix TypeError for invalid integer dates %Y%m%d with errors='ignore' (# GH 26583) (#26585)

Author: nathalier

doc/source/whatsnew/v0.25.0.rst

@@ -537,6 +537,7 @@ Datetimelike
 - Bug in :func:`to_datetime` which does not replace the invalid argument with ``NaT`` when error is set to coerce (:issue:`26122`)
 - Bug in adding :class:`DateOffset` with nonzero month to :class:`DatetimeIndex` would raise ``ValueError`` (:issue:`26258`)
 - Bug in :func:`to_datetime` which raises unhandled ``OverflowError`` when called with mix of invalid dates and ``NaN`` values with ``format='%Y%m%d'`` and ``error='coerce'`` (:issue:`25512`)
+- Bug in :func:`to_datetime` which raises ``TypeError`` for ``format='%Y%m%d'`` when called for invalid integer dates with length >= 6 digits with ``errors='ignore'``
 
 Timedelta
 ^^^^^^^^^

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

@@ -133,6 +133,25 @@ 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', [
+        # valid date, length == 8
+        [20121030, datetime(2012, 10, 30)],
+        # short valid date, length == 6
+        [199934, datetime(1999, 3, 4)],
+        # long integer date partially parsed to datetime(2012,1,1), length > 8
+        [2012010101, 2012010101],
+        # invalid date partially parsed to datetime(2012,9,9), length == 8
+        [20129930, 20129930],
+        # short integer date partially parsed to datetime(2012,9,9), length < 8
+        [2012993, 2012993],
+        # short invalid date, length == 4
+        [2121, 2121]])
+    def test_int_to_datetime_format_YYYYMMDD_typeerror(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):