[Tutor] Parsing problem
Paul McGuire
paul at alanweberassociates.com
Mon Jul 25 03:00:59 CEST 2005
Liam -
I just uploaded an update to pyparsing, version 1.3.2, that should fix the
problem with using nested Dicts. Now you won't need to use [0] to
dereference the "0'th" element, just reference the nested elements as a.b.c,
or a["b"]["c"].
-- Paul
-----Original Message-----
From: Liam Clarke [mailto:cyresse at gmail.com]
Sent: Sunday, July 24, 2005 10:21 AM
To: Paul McGuire
Cc: tutor at python.org
Subject: Re: [Tutor] Parsing problem
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
<mailto: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
<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.'
More information about the Tutor
mailing list