Issue #18037: Do not escape '\u' and '\U' in raw strings.

Lib/lib2to3/fixes/fix_unicode.py

@@ -28,8 +28,7 @@ class FixUnicode(fixer_base.BaseFix):
             return new
         elif node.type == token.STRING:
             val = node.value
-            if (not self.unicode_literals and val[0] in 'rR\'"' and
-                '\\' in val):
+            if not self.unicode_literals and val[0] in '\'"' and '\\' in val:
                 val = r'\\'.join([
                     v.replace('\\u', r'\\u').replace('\\U', r'\\U')
                     for v in val.split(r'\\')

Lib/lib2to3/tests/test_fixers.py

@@ -2830,7 +2830,7 @@ class Test_unicode(FixerTestCase):
         self.check(b, a)
 
         b = r"""r'\\\u20ac\U0001d121\\u20ac'"""
-        a = r"""r'\\\\u20ac\\U0001d121\\u20ac'"""
+        a = r"""r'\\\u20ac\U0001d121\\u20ac'"""
         self.check(b, a)
 
     def test_bytes_literal_escape_u(self):