Explicitly annotate this with `Final[str]` to make it work in mypyc 1.0.0+.
diff --git a/src/blib2to3/pgen2/tokenize.py b/src/blib2to3/pgen2/tokenize.py
index 257dbef4a19..a6353d154c9 100644
--- a/src/blib2to3/pgen2/tokenize.py
+++ b/src/blib2to3/pgen2/tokenize.py
@@ -425,7 +425,7 @@ def generate_tokens(
     logical line; continuation lines are included.
     """
     lnum = parenlev = continued = 0
-    numchars: Final = "0123456789"
+    numchars: Final[str] = "0123456789"
     contstr, needcont = "", 0
     contline: Optional[str] = None
     indents = [0]

I filed relevant mypyc bug here: https://github.com/mypyc/mypyc/issues/990

This is an error only in mypyc 1.0.0+