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I made a mistake in my description. In short, I get an extra match on "comparison". Updated above. |
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The last comparison is a successful match of comparison, it just comes as part of a failed match on chain. I made some changes to your code that make this process clearer (and might be easier to do than adding parse actions to trace the parsing behavior): exp_comparison = pp.Word(pp.alphanums) + pp.Word(pp.alphanums)
exp_comparison.set_parse_action(_comparison_action)
exp_comparison.set_name("exp_comparison").set_debug() # <-- added
exp_compchain = exp_comparison('comparison') + exp_chain('chain')
exp_compchain.set_parse_action(_compchain_action)
exp_compchain.set_name("exp_compchain").set_debug() # <-- addedwhich generates this output: Right now, the only way to conditionalize the comparison parse action based on whether the chain will match will be to do a lookahead using FollowedBy: exp_compchain = pp.FollowedBy(
exp_comparison().set_parse_action(None) + exp_chain().set_parse_action(None)
) + exp_comparison('comparison') + exp_chain('chain')I had to create copies of exp_comparison and exp_chain with no parse actions to put in the lookahead |
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That makes sense now. Thank you! |
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Can someone explain why this behaves the way it does?
It prints:
I'm expecting:
It seems to be calling the parse actions on failed matches.
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