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I'm wondering about whether using exceptions in the utility functions is misusing Python's exception handling system... Look at is_integer() for example. Is catching ValueError -- if the token cannot be converted -- a Pythonic thing? Or is it abusing exceptions for ordinary (non-exceptional) tokenizing?

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Looking at the usage of is_integer, personally I would write something like parse_integer(x: str) -> Optional[int], where the None variant represents a caught ValueError; this avoids parsing the integer twice but achieves basically the same effect (in a very similar style).

What would you propose as "more pythonic" here? Writing your own integer parsing code, by looking at the ASCII values of each character in the string?

It's suboptimal and you wouldn't want it for a production interpreter, but it's the lowest friction for leveraging what you get for free with Python to get something working correctly.

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