pyparsing-users

[Pyparsing] multiple tokens but no repeats

[Tim G. <tim...@si...>]

I'm trying to represent the logic that I wish to match 0 or more tokens, 
up to a maximum of 4 tokens, but I don't want any repeats of tokens 
already matched within the group of 4. How could I do that?

Thanks.
Tim

Re: [Pyparsing] multiple tokens but no repeats

[Ralph C. <ra...@in...>]

Hi Tim,

> I'm trying to represent the logic that I wish to match 0 or more
> tokens, up to a maximum of 4 tokens, but I don't want any repeats of
> tokens already matched within the group of 4. How could I do that?

I'm not sure if you can.  Perhaps there's a way to run your own
validation code as each attempt to grow the number of matches occurs?

Otherwise, since there's only four I'd enumerate the alternatives, e.g.

    a
    ab   ac   ad
    abc  abd  acb  acd  adb  adc
    abcd abdc acbd acdb adbc adcb

If I've got that right, there's 16 alternatives starting with `a'.  The
other three follow a similar pattern making 64 in total.  You could
factor out the common prefixes to speed up a Regex() a bit if you find
that just a dumb list seems slow.  Be sure to check whether order
determines whether it matches the longest possible, e.g. `abcz' should
match `abc' and not `a' or `ab'.

Cheers,


Ralph.

Re: [Pyparsing] multiple tokens but no repeats

[Paul M. <pt...@au...>]

Since these are supposed to represent the 4 fingers on your hand, can you
really have the out-of-order permutations?  Or are you really just looking
at the 16 values of corresponding to the binary values 0000 to 1111?  What
is the significance of a symbol meaning "pinky finger on opposite side of
index finger"?

-- Paul


-----Original Message-----
From: Ralph Corderoy [mailto:ra...@in...] 
Sent: Tuesday, November 20, 2007 11:10 AM
To: Tim Grove
Cc: pyp...@li...; Paul McGuire
Subject: Re: [Pyparsing] multiple tokens but no repeats 


Hi Tim,

> I'm trying to represent the logic that I wish to match 0 or more 
> tokens, up to a maximum of 4 tokens, but I don't want any repeats of 
> tokens already matched within the group of 4. How could I do that?

I'm not sure if you can.  Perhaps there's a way to run your own validation
code as each attempt to grow the number of matches occurs?

Otherwise, since there's only four I'd enumerate the alternatives, e.g.

    a
    ab   ac   ad
    abc  abd  acb  acd  adb  adc
    abcd abdc acbd acdb adbc adcb

If I've got that right, there's 16 alternatives starting with `a'.  The
other three follow a similar pattern making 64 in total.  You could factor
out the common prefixes to speed up a Regex() a bit if you find that just a
dumb list seems slow.  Be sure to check whether order determines whether it
matches the longest possible, e.g. `abcz' should match `abc' and not `a' or
`ab'.

Cheers,


Ralph.

Re: [Pyparsing] multiple tokens but no repeats

[W. M. B. <de...@de...>]

On Tue, Nov 20, 2007 at 03:24:34PM +0000, Tim Grove wrote:
> I'm trying to represent the logic that I wish to match 0 or more tokens, 
> up to a maximum of 4 tokens, but I don't want any repeats of tokens 
> already matched within the group of 4. How could I do that?

I would try setParseAction(), i.e. match 0 to 4 tokens and check
myself for duplication.