raise error in case of regex with groups and as_indexer=False

pandas/core/strings.py

@@ -477,7 +477,6 @@ def str_match(arr, pat, case=True, flags=0, na=np.nan, as_indexer=None):
     flags : int, default 0 (no flags)
         re module flags, e.g. re.IGNORECASE
     na : default NaN, fill value for missing values.
-    as_indexer : ignored
 
     Returns
     -------
@@ -495,7 +494,10 @@ def str_match(arr, pat, case=True, flags=0, na=np.nan, as_indexer=None):
 
     regex = re.compile(pat, flags=flags)
 
-    if as_indexer is not None:
+    if (as_indexer is False) and (regex.groups > 0):
+        raise ValueError("as_indexer=False with a pattern with groups is no "
+                         "longer supported. Use '.str.extract(pat)' instead")
+    elif as_indexer is not None:
         # Previously, this keyword was used for changing the default but
         # deprecated behaviour. This keyword is now no longer needed.
         warnings.warn("'as_indexer' keyword was specified but will be ignored;"
@@ -1558,7 +1560,7 @@ def contains(self, pat, case=True, flags=0, na=np.nan, regex=True):
         return self._wrap_result(result)
 
     @copy(str_match)
-    def match(self, pat, case=True, flags=0, na=np.nan, as_indexer=False):
+    def match(self, pat, case=True, flags=0, na=np.nan, as_indexer=None):
         result = str_match(self._data, pat, case=case, flags=flags, na=na,
                            as_indexer=as_indexer)
         return self._wrap_result(result)

pandas/tests/test_strings.py

@@ -580,6 +580,11 @@ def test_match(self):
         with tm.assert_produces_warning(UserWarning):
             result = values.str.match('.*BAD[_]+.*BAD', as_indexer=False)
         tm.assert_series_equal(result, exp)
+        with tm.assert_produces_warning(UserWarning):
+            result = values.str.match('.*(BAD[_]+).*(BAD)', as_indexer=True)
+        tm.assert_series_equal(result, exp)
+        self.assertRaises(ValueError, values.str.match, '.*(BAD[_]+).*(BAD)',
+                          as_indexer=False)
 
         # mixed
         mixed = Series(['aBAD_BAD', NA, 'BAD_b_BAD', True, datetime.today(),