Pyparsing: Non-greedy matching?

**Paul McGuire** · Jul 18 '05, 07:40 PM

Re: Pyparsing: Non-greedy matching?

"Peter Fein" <pfein@pobox.co m> wrote in message
news:mailman.86 32.1104454752.5 135.python-list@python.org ...[color=blue]
> I'm trying to use pyparsing write a screenscraper. I've got some
> arbitrary HTML text I define as opener & closer. In between is the HTML
> data I want to extract. However, the data may contain the same
> characters as used in the closer (but not the exact same text,
> obviously). I'd like to get the *minimal* amount of data between these.
>
> Here's an example (whitespace may differ):
>
> from pyparsing import *
>
> test=r"""<tr class="tableTop Space"><td></td></tr>
> <tr class="tableTit leDark"><td class="tableTit leDark">Job
> Information</td></tr><tr><td><tab le width="100%" border="0"
> cellspacing="3" ><tr>
> <td width="110" valign="top"><d iv align="right">< strong>Job Title:
> </strong></div></td>
> <td class="ccDispla yCell">Big Old <B
> STYLE="backgrou nd-color:#FFEF95"> Head Honcho</B> Boss Man</td></tr>
> <tr>
> <td width="110" valign="top"><d iv align="right">< strong>Employer :
> </strong></div></td>
> <td width="200" nowrap class="ccDispla yCell"><table>< tr><td colspan="2"
> valign="top">Gl obal Megacorp</td></tr></table></td><td>
> <script>
> function escapecomp(){
> }
> """
>
> data=Combine(On eOrMore(Word(pr intables)), adjacent=False,
> joinString=" ")
>
> title_open=Lite ral(r"""<td width="110" valign="top"><d iv
> align="right">< strong>Job Title: </strong></div></td>
> <td class="ccDispla yCell">""")
> title_open.supp ress()
>
> title_close=Lit eral(r"""</td>""")
> title_close.sup press()
>
> title=title_ope n + data + title_close
> title2=title_op en + (data | title_close)
>[color=green][color=darkred]
> >>> title.scanStrin g(test).next()[/color][/color]
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> StopIteration
>[color=green][color=darkred]
> >>> title2.scanStri ng(test).next()[/color][/color]
> ((['<td width="110" valign="top"><d iv align="right">< strong>Job Title:\n
> </strong></div></td>\n<td class="ccDispla yCell">', 'Big Old <B
> STYLE="backgrou nd-color:#FFEF95"> Head Honcho</B> Boss Man</td> </tr>
> <tr> <td width="110" valign="top"><d iv align="right">< strong>Employer :
> </strong></div></td> <td width="200" nowrap
> class="ccDispla yCell"><table>< tr><td colspan="2" valign="top">Gl obal
> Megacorp</td></tr></table></td> <td> <script> function escapecomp(){
> }'], {}), 182, 656)[color=green][color=darkred]
> >>>[/color][/color]
>
> I'd expected title to work, but it doesn't match at all. ;( In other
> test variants, title2 gives extra stuff at the end though not
> necessarily to the end of the string (due to unprintable characters,
> perhaps).
>
> I want a ParseResult more like:
> ['<td width="110" valign="top"><d iv align="right">< strong>Job Title:\n
> </strong></div></td>\n<td class="ccDispla yCell">', 'Big Old <B
> STYLE="backgrou nd-color:#FFEF95"> Head Honcho</B> Boss Man, '</td>']
>
> I sort of understand why title2 works as it does (the OneOrMore just
> slurps up everything), but for the life of me I can't figure out how to
> fix it. ;) Is there a way of writing something similar to RE's ".*?" ?
>
> --Pete
>
> --
> Peter Fein pfein@pobox.com 773-575-0694
>
> Basically, if you're not a utopianist, you're a schmuck. -J. Feldman[/color]

Peter -

Well you are correct, OneOrMore just keeps on slurping as long as it
continues to find matching text. Unlike RE's, it does not look ahead in the
RE to treat the next literal as a terminating expression.

In the examples that come with pyparsing, there is an HTML extractor
(getNTPservers. py) that uses a CharsNotIn("<") expression for the body of an
HTML tag. That works for the given case, but wont work for you - the body
of your tag also includes other HTML tags, such as <B>, so a CharsNotIn
would terminate before the complete body were extracted.

Assuming that your <td> tag wont contain any nested <td> tag, you could
define your data content as "everything up until I find '</td>'". For this
you can use pyparsing's SkipTo element. I think if you define data as:
data = SkipTo("</td>")
then your code should start working better.

There are a couple of other points on your sample code. Note that
suppress() is *not* a mutator, but actually a factory method - in
expr.suppress() , expr is not modified by suppress, but returns a Suppress
object wrapped around an expr. So in place of:
title_close=Lit eral(r"""</td>""")
title_close.sup press()
you should do
title_close=Lit eral(r"""</td>""").suppres s()
or
title_close=Lit eral(r"""</td>""")
title_close = title_close.sup press()

-- Paul

**Peter Fein** · Jul 18 '05, 07:40 PM

Re: Pyparsing: Non-greedy matching?

On 12/31/04 03:00 AM CST, "Paul McGuire" <ptmcg@austin.r r._bogus_.com>
sayeth:[color=blue]
> Assuming that your <td> tag wont contain any nested <td> tag, you
> could define your data content as "everything up until I find
> '</td>'". For this you can use pyparsing's SkipTo element. I think
> if you define data as:
> data = SkipTo("</td>")
> then your code should start working better.[/color]

Hey! It does! ;) I just worked up (note to googlers- don't do this):
goodchars=print ables.replace(" <", "")
good_ab="<" + (~Literal(r"""/td>""") + SkipTo(">", include=True))
good_ab.setDebu g(True)
simple=Word(goo dchars)
complex=Combine (simple | good_ab, adjacent=False, joinString="")
data=Combine(On eOrMore(complex ), adjacent=False, joinString=" ")
title4=title_op en+data

But that would break for closers with more than one ">". Need to stop
thinking like these are regexps. Thanks - this is a great tool. ;)

--
Peter Fein pfein@pobox.com 773-575-0694

Basically, if you're not a utopianist, you're a schmuck. -J. Feldman

Pyparsing: Non-greedy matching?

Pyparsing: Non-greedy matching?

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