pyparsing-users

[Pyparsing] Continue parsing on mismatches

[donn <don...@gm...>]

Hi,
How would I get PP to *continue* parsing a string, skipping over any 
mismatched (badly formed) patterns? Raising an exception that I can then 
continue from would be a bonus.


Here's my best effort so far to demo the thing:
-----

import pyparsing as PP

dot = PP.Literal(".")
comma = PP.Literal(",").suppress()

## A single digit like 0 really means 0.0 so the .0 is optional:
numberMaybeDotnumber = PP.Combine( PP.Word(PP.nums) + PP.Optional( dot + 
PP.Word(PP.nums) ) )

## I have seen Inkscape include E- in the string... e.g 0.8683224E-07, 
hence all the gumph in floater.
floater = PP.Combine(PP.Optional("-") + numberMaybeDotnumber + 
PP.Optional( PP.Literal("E") + PP.Literal("-") + PP.Word(PP.nums) ) )
floater.setParseAction(lambda toks:float(toks[0]))

open_bracket=PP.Literal("(").suppress()
close_bracket = PP.Literal(")").suppress()

opt_couple = PP.Optional( comma + floater + comma + floater )

## rotate( angle (,x,y) ) where ,x,y are optional.
rotate_command = "rotate" + open_bracket + PP.Group( floater + 
opt_couple ) + close_bracket

matrix_commands = rotate_command

phrase_matrix = PP.OneOrMore(PP.Group(matrix_commands))

##  right           wrong         right
##              PP stops here
##              with no error.
##                            I want this too
s="rotate(5,5,6) rotate(99,7) rotate(7)"

print phrase_matrix.parseString(s)

## swapped wrong/right at end to test.
s="rotate(5,5,6) rotate(99) rotate(7,7)"
print phrase_matrix.parseString(s)

-----

Output:
[['rotate', [5.0, 5.0, 6.0]]]
[['rotate', [5.0, 5.0, 6.0]], ['rotate', [99.0]]]

rotate( arg1 ) is okay.
rotate( arg1, arg2, arg3) is okay.
rotate( arg1,arg2 ) is wrong. I want to skip over that like it was never 
there (or raise an warning).
(same for rotate( ..empty.. ) and other mad patterns.)

Holding thumbs,
\d

Re: [Pyparsing] Continue parsing on mismatches

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

Donn -

See the embedded comments in this code:

import pyparsing as PP

# just get all the punctuation out of the way
dot,comma,open_bracket,close_bracket = map(PP.Suppress,".;()")

# I'm finding that complex items like real numbers just work better
# using a Regex than Combine'ing Words, Optionals, etc.
floater = PP.Regex(r"-?\d+(\.\d*)?([Ee][+-]?\d+)?")
floater.setParseAction(lambda toks:float(toks[0]))

# define a permissive expression for rotate_command, then do additional
# validation in the parse action
rotate_command = "rotate" + \
    open_bracket + PP.Optional(PP.delimitedList(floater))("args") + \
    close_bracket

def validate_rotate_args(s,l,tokens):
    numargs = len(tokens.args)
    if not(numargs == 1 or numargs == 3):
        raise PP.ParseException(s,l,"wrong number of args")
    # convert generic 'args' name to specific field names
    tokens["angle"] = tokens.args[0]
    tokens["pivot"] = tokens.args[1:3]
    del tokens["args"]
    
rotate_command.setParseAction(validate_rotate_args)


>From here, you could use scanString or searchString to return just the valid
commands:

for rotation in rotate_command.searchString(s):
    print rotation.dump()

Gives:

 ['rotate', 5.0, 5.0, 6.0]
- angle: 5.0
- pivot: [5.0, 6.0]
['rotate', 7.0]
- angle: 7.0
- pivot: []

The parseAction has detected that "rotate(99,7)" has the wrong number of
arguments.

There's not really any way to emit a warning while parsing - either the
parse matches, or it raises a ParseException.

-- Paul

Re: [Pyparsing] Continue parsing on mismatches

[donn <don...@gm...>]

On 07/03/2010 19:13, Paul McGuire wrote:
> See the embedded comments in this code:
Paul,
You save me annually! And so many new tricks. PP.delimitedList! 
Whodathunkit? :D

  Thanks once again. I am working on extending my previous SVG parser to 
be far more robust. I shall certainly post the source on the Pyparsing 
wiki when it's done.

Now, lemme go hack the the code you sent.

Best,
\d

-- 
Fonty Python and Things! -- http://otherwise.relics.co.za/wiki/Software