Re: [Pyparsing] grammar with bad performance (with examples :))

[david <asd...@gn...>]

On Mon, 10 Dec 2007 10:53:13 -0600, Paul McGuire wrote:

> David -
> 
> Here is a modified version of your program, that runs for me in 0.05
> seconds or so.

Paul, 
Thank you very much, your explanation is excellent, and the new grammar 
works like a charms :)

> The main problem was your universal use of Or instead of MatchFirst. 
> Using Or in the definition of OPERATOR is not so big a problem, but you
> can convert to MatchFirst if you are careful about the ordering of your
> operators.  And the operators may as well be Literals, and not Keywords,
> since Keyword only looks for boundary alphanumeric characters, not
> symbols or whitespace.

I understand the performance implications between Or and MatchFirst, but 
I still don't understand why Literals are faster than of Keywords.

> Is there any reason you choose the
> 
> OPERATOR = psg.Or([EQUAL, NOT_EQUAL, CONTAINS, NOT_CONTAINS, STARTWITH])
> 
> style, instead of using the built-in operators:
> 
> OPERATOR = EQUAL ^ NOT_EQUAL ^ CONTAINS ^ NOT_CONTAINS ^ STARTWITH
> 
> or even better:
> 
> OPERATOR = STARTWITH | EQUAL | NOT_EQUAL | CONTAINS | NOT_CONTAINS

Writing grammars is not my business, thanks to pyparsing's simplicity I 
wrote my first grammar (the one your tune) months ago in one day; I tend 
to prefer a more readable syntax for non repetitive tasks.

Thank you
david