fixup! Replace percent formatting

Author: snejus

beets/util/functemplate.py

@@ -296,9 +296,6 @@ def __init__(self, string, in_argument=False):
         GROUP_CLOSE,
         ESCAPE_CHAR,
     )
-    special_char_re = re.compile(
-        rf"[{''.join(re.escape(c) for c in special_chars)}]|\Z"
-    )
     escapable_chars = (SYMBOL_DELIM, FUNC_DELIM, GROUP_CLOSE, ARG_SEP)
     terminator_chars = (GROUP_CLOSE,)
 
@@ -310,20 +307,18 @@ def parse_expression(self):
         """
         # Append comma (ARG_SEP) to the list of special characters only when
         # parsing function arguments.
-        extra_special_chars = ()
-        special_char_re = self.special_char_re
-        if self.in_argument:
-            special_chars = (*self.special_chars, ARG_SEP)
-            special_char_re = re.compile(
-                rf"[{''.join(map(re.escape, special_chars))}]|\Z"
-            )
+        extra_special_chars = (ARG_SEP,) if self.in_argument else ()
+        special_chars = (*self.special_chars, *extra_special_chars)
+        special_char_re = re.compile(
+            rf"[{''.join(map(re.escape, special_chars))}]|\Z"
+        )
 
         text_parts = []
 
         while self.pos < len(self.string):
             char = self.string[self.pos]
 
-            if char not in self.special_chars + extra_special_chars:
+            if char not in special_chars:
                 # A non-special character. Skip to the next special
                 # character, treating the interstice as literal text.
                 next_pos = (