You can disable the backtracking within an a, b, c, or d by using the '-'
operator instead of '+':
a = a_header - a_data
b = b_header - b_data
c = c_header - c_data
d = d_header - d_data
I think this will accomplish what you wanted with Required.
-- Paul
-----Original Message-----
From: Russell Dill [mailto:Rus...@as...]
Sent: Wednesday, September 28, 2011 12:32 AM
To: pyp...@li...
Subject: [Pyparsing] Required Class?
I have some text I'm parsing with headers and then data. The
header/data groups can be in any order, aba, aabbba, acbd, bdacaa, etc
(Where the letter represents a header type followed by its data). So
overall, I have something like:
a = a_header + a_data
b = b_header + b_data
c = c_header + c_data
d = d_header + d_data
ZeroOrMore(a | b | c | d) + EndTag
Now, if a_header exists, but a_data is malformed, I get an error that
it expected EndTag. For easier debugging, I'd like the error to make
more sense, so:
a = a_header + Required(a_data) where:
class Required(ParseElementEnhance):
def __init__(self, exprs):
super(Required, self).__init__(exprs)
def parseImpl(self, instring, loc, doActions=True):
try:
loc, tokens = self.expr._parse(instring, loc, doActions,
callPreParse=False)
except ParseException as e:
raise ParseFatalException(e)
return loc, tokens
Is this the best way to go about this goal?
Is there instead a better way of saying any number of any of these
expressions in any order?
If at least one (or exactly one) 'c' expression is required, is there
a way of denoting that?
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