[Python] Syntactically required and semantically relevant tokens in Python grammars

I am trying to parse code into AST. I want to keep minimum keywords and delimiters in the AST while keeping the semantics.

In Python function definition def foo():, the last : is syntactically required but also redundant in semantic structure, which means it can be omitted in the AST and reconstructed from the AST.

But I also notice that the : in slice expression start:end is semantically relevant that it can't be omitted in the AST. Removing it will lead to ambiguous semantic; take index: and :index, for example.

I wonder if there are more keywords or delimiters in Python grammar that share a similar property to : in slice expressions?

Tree-sitter is what I am using for parsing.

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