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