Strange peek behaviour/generator exception handling? about parsy HOT 4 OPEN

Edit: So to restate this in a clearer manner: As far as I can tell, python doesn't let you catch exceptions raised from inside a generator, because they are converted into stopping the generator.

All the stackoverflow posts I've looked at so far suggest yielding an exception object from a generator instead of having it raised, which I don't really like, and might require rearchitecting parsy?

I'm going to try to see if I can write a wrapper function that will catch exceptions and return them in this form, so at least it can be done on a case by case basis, but will look less nice.

from parsy.

To be clear, help on the above would be appreciated, I'm winging this.

from parsy.

If the above is true I'm not quite sure I get how the normal case works, but being unable to figure out how to implement something better, I found a workaround:

I think I've temporarily worked around this by modifying the peek implementation to signal the end of the stream with None (I should probably create a more descriptive symbol instead);

def peek_with_none(parser): #To work around the cant raise exception from yield issue
    @Parser
    def peek_parser(stream, index):
        if index == len(stream):
            #bail early instead of raising a ParseError, or something
            return Result.success(index, None)

        result = parser(stream, index)
        if result.status:
            return Result.success(index, result.value)
        else:
            return result
    return peek_parser

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I completely forgot I ran into this exact issue and did it again.
I think the problem is that wrapping a yield in a try/except doesn't catch the error because it's not actually "running" in the context where the try/except is. It's returning a value which gets run somewhere else.

I haven't actually figured out how to make this work but it probably involves writing a @parser. I worked around my issue temporarily by using a peek that wouldnt fail and .map()-ing a conditional function over the result to check if continuing is ok.

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