In the Python.asdl syntax description, the file asserts that Dict literal keys have type expr*. This is false. keys can be optional.

In the ast documentation for Python:

• https://docs.python.org/3/library/ast.html#ast.Dict it is made clear that:

When doing dictionary unpacking using dictionary literals the expression to be expanded goes in the values list, with a None at the corresponding position in keys.

Hence, keys is really a expr?* and not a expr*.

Linked PRs

• gh-131421: fix ASDL grammar for Dict to have an expr?* keys field #131419
• gh-131421: Fix ASDL tests #133408
• gh-131421: Fix ASDL kw_defaults being expr* instead of expr?* (+ fix docs ASDL highlighting) #133773