Pyparsing: Non-greedy matching?

[Paul McGuire]

"Peter Fein" <pfein at pobox.com> wrote in message
news:mailman.8632.1104454752.5135.python-list at python.org...
> 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="tableTopSpace"><td></td></tr>
> <tr class="tableTitleDark"><td class="tableTitleDark">Job
> Information</td></tr><tr><td><table width="100%" border="0"
> cellspacing="3"><tr>
> <td width="110" valign="top"><div align="right"><strong>Job Title:
>       </strong></div></td>
> <td class="ccDisplayCell">Big Old <B
> STYLE="background-color:#FFEF95">Head Honcho</B> Boss Man</td></tr>
> <tr>
> <td width="110" valign="top"><div align="right"><strong>Employer:
>         </strong></div></td>
> <td width="200" nowrap class="ccDisplayCell"><table><tr><td colspan="2"
> valign="top">Global Megacorp</td></tr></table></td><td>
>     <script>
>     function escapecomp(){
>     }
> """
>
> data=Combine(OneOrMore(Word(printables)), adjacent=False,
> joinString=" ")
>
> title_open=Literal(r"""<td width="110" valign="top"><div
> align="right"><strong>Job Title:      </strong></div></td>
> <td class="ccDisplayCell">""")
> title_open.suppress()
>
> title_close=Literal(r"""</td>""")
> title_close.suppress()
>
> title=title_open + data + title_close
> title2=title_open + (data | title_close)
>
> >>> title.scanString(test).next()
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> StopIteration
>
> >>> title2.scanString(test).next()
> ((['<td width="110" valign="top"><div align="right"><strong>Job Title:\n
>      </strong></div></td>\n<td class="ccDisplayCell">', 'Big Old <B
> STYLE="background-color:#FFEF95">Head Honcho</B> Boss Man</td> </tr>
> <tr> <td width="110" valign="top"><div align="right"><strong>Employer:
> </strong></div></td> <td width="200" nowrap
> class="ccDisplayCell"><table><tr><td colspan="2" valign="top">Global
> Megacorp</td></tr></table></td> <td> <script> function escapecomp(){
> }'], {}), 182, 656)
> >>>
>
> 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"><div align="right"><strong>Job Title:\n
>      </strong></div></td>\n<td class="ccDisplayCell">', 'Big Old <B
> STYLE="background-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 at pobox.com                 773-575-0694
>
> Basically, if you're not a utopianist, you're a schmuck. -J. Feldman

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=Literal(r"""</td>""")
    title_close.suppress()
you should do
    title_close=Literal(r"""</td>""").suppress()
or
    title_close=Literal(r"""</td>""")
    title_close = title_close.suppress()

-- Paul