pyparsing

I have some sentences that I need to convert to regex code and I was trying to use Pyparsing for it. The sentences are basically search rules, telling us what to search for. Examples of sentences - LINE_CONTAINS this is a phrase -this is an example search rule telling that the line you are searching on should have the phrase this is a phrase LINE_STARTSWITH However we - this is an example search rule telling that the line you are searching on should start with the phrase However we The rules can be combined too, like- LINE_CONTAINS phrase one BEFORE {phrase2 AND phrase3} AND LINE_STARTSWITH

>>> g = MatchFirst( Literal("scoobydoo"), Literal("scooby") ) >>> g.parseString( "scooby" ) pyparsing.ParseException: Expected "scoobydoo" (at char 0), (line:1, col:1) Is the ParseException thrown because the scooby has already been consumed in the character stream & thus the parser cannot backtrack ? I'm looking for a detailed implementation explanation for this. At the moment, I consider this a bug because why would the parser short-circuit the matching since it has not search all the choices in production rule. UPDATE : Seems like MatchFirst is not exactly equivalent to | operator. Why ? >>

I have a simple example where I would like to parse 2 lines of data. In [1] from pyparsing import Word, nums, OneOrMore, Optional, Suppress, alphanums, LineEnd, LineStart Float = Word(nums + '.' + '-') Name = Word(alphanums) Line = OneOrMore(Float)('data') + Suppress(Optional(';')) + Optional('%') + Optional(Name)('name') Lines = OneOrMore(Line + LineEnd()) string = ''' 1 10 0 T20 1 76 0 T76 ''' result = Lines.parseString(string) In [2] result Out[2] (['1', '10', '0', 'T20', '\n', '1', '76', '0', 'T76', '\n'], {'data': [(['1', '10', '0'], {}), (['1', '76', '0'], {})], 'name': ['T20', 'T76']})