Convert groups to string to prevent mypy for shouting

src/black/linegen.py

@@ -261,7 +261,6 @@ def visit_factor(self, node: Node) -> Iterator[Line]:
 
     def visit_STRING(self, leaf: Leaf) -> Iterator[Line]:
         if Preview.hex_codes_in_unicode_sequences in self.mode:
-            # Preview style only
             normalize_unicode_escape_sequences(leaf)
 
         if is_docstring(leaf) and "\\\n" not in leaf.value:

src/black/strings.py

@@ -22,10 +22,10 @@
 FIRST_NON_WHITESPACE_RE: Final = re.compile(r"\s*\t+\s*(\S)")
 UNICODE_RE = re.compile(
     r"(\\+)("
-    r"(u([a-zA-Z0-9]{4}))"
-    r"|(U([a-zA-Z0-9]{0,8}))"
-    r"|(x([a-zA-Z0-9]{2}))"
-    r"|(N\{([a-zA-Z0-9]{2})\})"
+    r"(u([a-zA-Z0-9]{4}))"  # Formatting 16-bit unicodes i.e. \uxxxx
+    r"|(U([a-zA-Z0-9]{0,8}))"  # Formatting 32-bit unicodes i.e. \Uxxxxxxxx
+    r"|(x([a-zA-Z0-9]{2}))"  # Formatting unicodes in format of \xhh
+    r"|(N\{([a-zA-Z0-9]{2})\})"  # Formatting named unicodes in format of \N{name}
     r")"
 )
 
@@ -253,23 +253,24 @@ def normalize_unicode_escape_sequences(leaf: Leaf) -> None:
     text = leaf.value
     prefix = get_string_prefix(text)
 
-    def replace(m: Match[AnyStr]) -> AnyStr:
+    def replace(m: Match[AnyStr]) -> str:
         groups = m.groups()
+        back_slashes = str(groups[0])
 
-        if len(groups[0]) % 2 == 0 or prefix == "r":
-            return groups[0] + groups[1]
+        if len(back_slashes) % 2 == 0 or prefix == "r":
+            return back_slashes + str(groups[1])
 
         if groups[2]:
             # \u
-            return groups[0] + "u" + groups[3].lower()
+            return back_slashes + "u" + str(groups[3].lower())
         elif groups[4]:
             # \U
-            return groups[0] + "U" + groups[5].lower()
+            return back_slashes + "U" + str(groups[5].lower())
         elif groups[6]:
             # \x
-            return groups[0] + "x" + groups[7].lower()
+            return back_slashes + "x" + str(groups[7].lower())
         else:
             # \N{}
-            return groups[0] + "N{" + groups[9].upper() + "}"
+            return back_slashes + "N{" + str(groups[9].upper()) + "}"
 
     leaf.value = re.sub(UNICODE_RE, replace, text)

test.py

@@ -0,0 +1,10 @@
+x = "\x1f"
+x = "\\x1B"
+x = "\\\x1b"
+x = "\U0001f60e"
+x = "\u0001F60E"
+x = r"\u0001F60E"
+x = "don't format me"
+x = "\xa3"
+x = "\u2717"
+x = "\N{OX}\N{OX}"