Fix IndexError in strip_whitespace for collapsed parenthesis groups

AUTHORS

@@ -16,6 +16,7 @@ Alphabetical list of contributors:
 * ali-tny <aliteeney@googlemail.com>
 * andrew deryabin <github@djsf.com>
 * Andrew Tipton <andrew.tipton@compareglobalgroup.com>
+* Anshul Singh <https://github.com/ekanshul>
 * atronah <atronah.ds@gmail.com>
 * casey <casey@cloudera.com>
 * Cauê Beloni <cbeloni@gmail.com>

CHANGELOG

@@ -1,7 +1,8 @@
 Development Version
 -------------------
 
-Nothing yet.
+* Fix IndexError in ``strip_whitespace`` for parenthesis groups that
+  collapse to a single nested child (e.g. ``( AS )``). See issue885.
 
 
 Release 0.6.0 (Aug 13, 2026)

sqlparse/filters/others.py

@@ -112,13 +112,18 @@ def _stripws_identifierlist(self, tlist):
         return self._stripws_default(tlist)
 
     def _stripws_parenthesis(self, tlist):
+        # Well-formed groups look like "(", content..., ")". Some inputs
+        # (e.g. "( AS )") collapse to a single nested child, so there is
+        # no tokens[1] / tokens[-2] to strip.
+        if len(tlist.tokens) < 3:
+            return self._stripws_default(tlist)
         while tlist.tokens[1].is_whitespace:
             tlist.tokens.pop(1)
         while tlist.tokens[-2].is_whitespace:
             tlist.tokens.pop(-2)
         if tlist.tokens[-2].is_group:
             # save to remove the last whitespace
-            while tlist.tokens[-2].tokens[-1].is_whitespace:
+            while tlist.tokens[-2].tokens and tlist.tokens[-2].tokens[-1].is_whitespace:
                 tlist.tokens[-2].tokens.pop(-1)
         self._stripws_default(tlist)
 

tests/test_regressions.py

@@ -285,6 +285,12 @@ def test_issue213_leadingws():
     assert sqlparse.format(sql, strip_whitespace=True) == "select * from foo"
 
 
+def test_issue885_strip_ws_malformed_parenthesis():
+    # Parenthesis grouping can collapse "( AS )" to a single nested child.
+    # strip_whitespace must not assume tokens[1] / tokens[-2] exist.
+    assert sqlparse.format("( AS )", strip_whitespace=True) == "( AS )"
+
+
 def test_issue227_gettype_cte():
     select_stmt = sqlparse.parse('SELECT 1, 2, 3 FROM foo;')
     assert select_stmt[0].get_type() == 'SELECT'