[Tutor] Parsing problem

[Liam Clarke]

Hi Paul, 

That is fantastic. It works, and using that pp.group is the key with the 
nested braces. 

I just ran this on the actual file after adding a few more possible values 
inside the group, and it parsed the entire header structure rather nicely.

Now this will probably sound silly, but from the bit 

header = {...
...
}

it continues on with 

province = {...
} 

and so forth. 

Now, once it reads up to the closing bracket of the header section, it 
returns that parsed nicely. 
Is there a way I can tell it to continue onwards? I can see that it's 
stopping at one group.

Pyparsing is wonderful, but boy... as learning curves go, I'm somewhat over 
my head.

I've tried this - 

Code http://www.rafb.net/paste/results/3Dm7FF35.html
Current data http://www.rafb.net/paste/results/3cWyt169.html

assignment << (pp.OneOrMore(pp.Group( LHS + EQUALS + RHS ))) 

to try and continue the parsing, but no luck.

I've been running into the 

File "c:\python24\Lib\site-packages\pyparsing.py", line 1427, in parseImpl
raise maxException
pyparsing.ParseException: Expected "}" (at char 742), (line:35, col:5) 

hassle again. From the CPU loading, I'm worried I've got myself something 
very badly recursive going on, but I'm unsure of how to use validate()

I've noticed that a few of the sections in between contain values like this 
- 

foo = { BAR = { HUN = 10 SOB = 6 } oof = { HUN = { } SOB = 4 } }

and so I've stuck pp.empty into my RHS possible values. What unintended side 
effects may I get from using pp.empty? From the docs, it sounds like a 
wildcard token, rather than matching a null.

Using pp.empty has resolved my apparent problem with empty {}'s causing my 
favourite exception, but I'm just worried that I'm casting my net too wide.

Oh, and, if there's a way to get a 'last line parsed' value so as to start 
parsing onwards, it would ease my day, as the only way I've found to get the 
whole thing parsed is to use another x = { ... } around the whole of the 
data, and now, I'm only getting the 'x' returned, so if I could parse by 
section, it would help my understanding of what's happening. 

I'm still trial and error-ing a bit too much at the moment.

Regards, 

Liam Clarke




On 7/24/05, Paul McGuire <paul at alanweberassociates.com> wrote:
> 
> Liam -
> 
> Glad you are sticking with pyparsing through some of these idiosyncracies!
> 
> One thing that might simplify your life is if you are a bit more strict on
> specifying your grammar, especially using pp.printables as the character 
> set
> for your various words and values. Is this statement really valid?
> 
> Lw)r*)*dsflkj = sldjouwe)r#jdd
> 
> According to your grammar, it is. Also, by using printables, you force 
> your
> user to insert whitespace between the assignment target and the equals 
> sign.
> I'm sure your users would like to enter a quick "a=1" once in a while, but
> since there is no whitespace, it will all be slurped into the left-hand 
> side
> identifier.
> 
> Let's create two expressions, LHS and RHS, to dictate what is valid on the
> left and right-hand side of the equals sign. (Well, it turns out I create 
> a
> bunch of expressions here, in the process of defining LHS and RHS, but
> hopefullly, this will make some sense):
> 
> EQUALS = pp.Suppress("=")
> LBRACE = pp.Suppress("{")
> RBRACE = pp.Suppress("}")
> identifier = pp.Word(pp.alphas, pp.alphanums + "_")
> integer = pp.Word(pp.nums+"-+", pp.nums)
> assignment = pp.Forward()
> LHS = identifier
> RHS = pp.Forward().setName("RHS")
> RHS << ( pp.dblQuotedString ^ identifier ^ integer ^ pp.Group( LBRACE +
> pp.OneOrMore(assignment) + RBRACE ) )
> assignment << pp.Group( LHS + EQUALS + RHS )
> 
> I leave it to you to flesh out what other possible value types can be
> included in RHS.
> 
> Note also the use of the Group. Try running this snippet with and without
> Group and see how the results change. I think using Group will help you to
> build up a good parse tree for the matched tokens.
> 
> Lastly, please note in the '<<' assignment to RHS that the expression is
> enclosed in parens. I originally left this as
> 
> RHS << pp.dblQuotedString ^ identifier ^ integer ^ pp.Group( LBRACE +
> pp.OneOrMore(assignment) + RBRACE )
> 
> And it failed to match! A bug! In my own code! The shame...
> 
> This fails because '<<' has a higher precedence then '^', so RHS only 
> worked
> if it was handed a quoted string. Probably good practice to always enclose
> in quotes the expression being assigned to a Forward using '<<'.
> 
> -- Paul
> 
> 
> -----Original Message-----
> From: Liam Clarke [mailto:cyresse at gmail.com]
> Sent: Saturday, July 23, 2005 9:03 AM
> To: Paul McGuire
> Cc: tutor at python.org
> Subject: Re: [Tutor] Parsing problem
> 
> *sigh* I just read the documentation more carefully and found the 
> difference
> between the
> | operator and the ^ operator.
> 
> Input -
> 
> j = { line = { foo = 10 bar = 20 } }
> 
> New code
> 
> sel = pp.Forward()
> values = ((pp.Word(pp.printables) + pp.Suppress("=") +
> pp.Word(pp.printables)) ^ sel)
> sel << (pp.Word(pp.printables) + pp.Suppress("=") + pp.Suppress("{") +
> pp.OneOrMore(values) + pp.Suppress("}"))
> 
> Output -
> 
> (['j', 'line', 'foo', '10', 'bar', '20'], {})
> 
> My apologies for the deluge.
> 
> Regards,
> 
> Liam Clarke
> 
> 
> On 7/24/05, Liam Clarke <cyresse at gmail.com> wrote:
> 
> Hmmm... just a quick update, I've been poking around and I'm
> obviously making some error of logic.
> 
> Given a line -
> 
> f = "j = { line = { foo = 10 bar = 20 } }"
> 
> And given the following code -
> 
> select = pp.Forward()
> select <<
> pp.Word(pp.printables) + pp.Suppress("=") + pp.Suppress("{") +
> pp.OneOrMore( (pp.Word(pp.printables) + pp.Suppress("=") +
> pp.Word(pp.printables) ) | select ) + pp.Suppress("}")
> 
> sel.parseString(f) gives -
> 
> (['j', 'line', '{', 'foo', '10', 'bar', '20'], {})
> 
> So I've got a bracket sneaking through there. Argh. My brain hurts.
> 
> Is the | operator an exclusive or?
> 
> Befuddled,
> 
> Liam Clarke
> 
> 
> 
> On 7/23/05, Liam Clarke <cyresse at gmail.com > wrote:
> 
> Howdy,
> 
> I've attempted to follow your lead and have started from
> scratch, I could just copy and paste your solution (which works pretty
> well), but I want to understand what I'm doing *grin*
> 
> However, I've been hitting a couple of ruts in the path to
> enlightenment. Is there a way to tell pyparsing that to treat specific
> escaped characters as just a slash followed by a letter? For the time 
> being
> I've converted all backslashes to forwardslashes, as it was choking on \a 
> in
> a file path.
> 
> But my latest hitch, takes this form (apologies for large
> traceback)
> 
> Traceback (most recent call last):
> File "<interactive input>", line 1, in ?
> File "parse.py", line 336, in parse
> parsedEntries = dicts.parseString(test_data)
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 616, in parseString
> loc, tokens = self.parse( instring.expandtabs(), 0 )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 558, in parse
> loc,tokens = self.parseImpl( instring, loc, doActions )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 1518, in parseImpl
> return self.expr.parse( instring, loc, doActions )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 558, in parse
> loc,tokens = self.parseImpl( instring, loc, doActions )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 1367, in parseImpl
> loc, exprtokens = e.parse( instring, loc, doActions )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 558, in parse
> loc,tokens = self.parseImpl( instring, loc, doActions )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 1518, in parseImpl
> return self.expr.parse( instring, loc, doActions )
> File "c:\python24\Lib\site-packages\pyparsing.py", line
> 560, in parse
> raise ParseException, ( instring, len(instring),
> self.errmsg, self )
> 
> ParseException: Expected "}" (at char 9909), (line:325,
> col:5)
> 
> The offending code can be found here (includes the data) -
> http://www.rafb.net/paste/results/L560wx80.html
> 
> It's like pyparsing isn't recognising a lot of my "}"'s, as
> if I add another one, it throws the same error, same for adding another
> two...
> 
> No doubt I've done something silly, but any help in finding
> the tragic flaw would be much appreciated. I need to get a parsingResults
> object out so I can learn how to work with the basic structure!
> 
> Much regards,
> 
> Liam Clarke
> 
> 
> 
> On 7/21/05, Paul McGuire < paul at alanweberassociates.com
> <mailto:paul at alanweberassociates.com> > wrote:
> 
> Liam, Kent, and Danny -
> 
> It sure looks like pyparsing is taking on a life of
> its own! I can see I no
> longer am the only one pitching pyparsing at some of
> these applications!
> 
> Yes, Liam, it is possible to create dictionary-like
> objects, that is,
> ParseResults objects that have named values in them.
> I looked into your
> application, and the nested assignments seem very
> similar to a ConfigParse
> type of structure. Here is a pyparsing version that
> handles the test data
> in your original post (I kept Danny Yoo's recursive
> list values, and added
> recursive dictionary entries):
> 
> --------------------------
> import pyparsing as pp
> 
> listValue = pp.Forward()
> listSeq = pp.Suppress ('{') +
> pp.Group(pp.ZeroOrMore(listValue)) +
> pp.Suppress('}')
> listValue << (
> pp.dblQuotedString.setParseAction(pp.removeQuotes) |
> pp.Word(pp.alphanums) | listSeq )
> 
> keyName = pp.Word( pp.alphas )
> 
> entries = pp.Forward()
> entrySeq = pp.Suppress('{') +
> pp.Group(pp.OneOrMore(entries)) +
> pp.Suppress('}')
> entries << pp.Dict(
> pp.OneOrMore (
> pp.Group( keyName + pp.Suppress('=')
> + (entrySeq |
> listValue) ) ) )
> --------------------------
> 
> 
> Dict is one of the most confusing classes to use,
> and there are some
> examples in the examples directory that comes with
> pyparsing (see
> dictExample2.py), but it is still tricky. Here is
> some code to access your
> input test data, repeated here for easy reference:
> 
> --------------------------
> testdata = """\
> country = {
> tag = ENG
> ai = {
> flags = { }
> combat = { DAU FRA ORL PRO }
> continent = { }
> area = { }
> region = { "British Isles" "NorthSeaSea"
> "ECAtlanticSea" "NAtlanticSea"
> "TagoSea" "WCAtlanticSea" }
> war = 60
> ferocity = no
> }
> }
> """
> parsedEntries = entries.parseString(testdata)
> 
> def dumpEntries(dct,depth=0):
> keys = dct.keys()
> keys.sort()
> for k in keys:
> print (' '*depth) + '- ' + k + ':',
> if isinstance(dct[k],pp.ParseResults):
> if dct[k][0].keys():
> print
> dumpEntries(dct[k][0],depth+1)
> else:
> print dct[k][0]
> else:
> print dct[k]
> 
> dumpEntries( parsedEntries )
> 
> print
> print parsedEntries.country[0].tag
> print parsedEntries.country[0].ai[0].war
> print parsedEntries.country[0].ai[0].ferocity
> --------------------------
> 
> This will print out:
> 
> --------------------------
> - country:
> - ai:
> - area: []
> - combat: ['DAU', 'FRA', 'ORL', 'PRO']
> - continent: []
> - ferocity: no
> - flags: []
> - region: ['British Isles', 'NorthSeaSea',
> 'ECAtlanticSea',
> 'NAtlanticSea', 'TagoSea', 'WCAtlanticSea']
> - war: 60
> - tag: ENG
> 
> ENG
> 60
> No
> --------------------------
> 
> But I really dislike having to dereference those
> nested values using the
> 0'th element. So I'm going to fix pyparsing so that
> in the next release,
> you'll be able to reference the sub-elements as:
> 
> print parsedEntries.country.tag
> print parsedEntries.country.ai.war
> print parsedEntries.country.ai.ferocity
> 
> This *may* break some existing code, but Dict is not
> heavily used, based on
> feedback from users, and this may make it more
> useful in general, especially
> when data parses into nested Dict's.
> 
> Hope this sheds more light than confusion!
> -- Paul McGuire
> 
> _______________________________________________
> Tutor maillist - Tutor at python.org
> <mailto:Tutor at python.org>
> http://mail.python.org/mailman/listinfo/tutor
> 
> 
> 
> 
> 
> --
> 'There is only one basic human right, and that is to do as
> you damn well please.
> And with it comes the only basic human duty, to take the
> consequences.'
> 
> 
> 
> 
> --
> 'There is only one basic human right, and that is to do as you damn
> well please.
> And with it comes the only basic human duty, to take the
> consequences.'
> 
> 
> 
> 
> --
> 'There is only one basic human right, and that is to do as you damn well
> please.
> And with it comes the only basic human duty, to take the consequences.'
> 
> 


-- 
'There is only one basic human right, and that is to do as you damn well 
please.
And with it comes the only basic human duty, to take the consequences.'
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