Update expression.py

Author: BobTheBuidler

mypyc/irbuild/expression.py

@@ -9,7 +9,7 @@
 import math
 from collections.abc import Sequence
 from functools import partial
-from typing import Callable, Union
+from typing import Callable, Union, cast
 
 from mypy.nodes import (
     ARG_NAMED,
@@ -1029,7 +1029,9 @@ def constant_fold_expr_or_tuple(
             return value
         if not isinstance(expr, TupleExpr):
             return None
-        folded = tuple(map(partial(constant_fold_expr_or_tuple, builder), expr.items))
+        folded: ConstantValueTuple = tuple(
+            map(partial(constant_fold_expr_or_tuple, builder), expr.items)
+        )
         return folded if None not in folded else None
 
     result = {}