Issue #13938: 2to3 converts StringTypes to a tuple. Patch from Mark Hammond.

Lib/lib2to3/fixes/fix_types.py

@@ -42,7 +42,7 @@ _TYPE_MAPPING = {
         'NotImplementedType' : 'type(NotImplemented)',
         'SliceType' : 'slice',
         'StringType': 'bytes', # XXX ?
-        'StringTypes' : 'str', # XXX ?
+        'StringTypes' : '(str,)', # XXX ?
         'TupleType': 'tuple',
         'TypeType' : 'type',
         'UnicodeType': 'str',

Lib/lib2to3/tests/test_fixers.py

@@ -3322,6 +3322,10 @@ class Test_types(FixerTestCase):
         a = """type(None)"""
         self.check(b, a)
 
+        b = "types.StringTypes"
+        a = "(str,)"
+        self.check(b, a)
+
 class Test_idioms(FixerTestCase):
     fixer = "idioms"
 

Misc/NEWS

@@ -13,6 +13,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #13938: 2to3 converts StringTypes to a tuple. Patch from Mark Hammond.
+
 - Issue #8585: improved tests for zipimporter2. Patch from Mark Lawrence.
 
 - Issue #18622: unittest.mock.mock_open().reset_mock would recurse infinitely.