To indicate that a particular parse expression may be empty, pyparsing includes the Optional element.
Change: pp.delimitedList(withquotes | withoutquotes) + \ to: pp.Optional( pp.delimitedList(withquotes | withoutquotes) ) + \ and I think this will have the desired effect. -- Paul <gry@ll.mit.edu> wrote in message news:[EMAIL PROTECTED] > [python 2.3.3, pyparsing 1.3] > I have: > > def unpack_sql_array(s): > # unpack a postgres "array", e.g. "{'w1','w2','w3'}" into a > list(str) > import pyparsing as pp > withquotes = pp.dblQuotedString.setParseAction(pp.removeQuotes) > withoutquotes = pp.CharsNotIn('",{}') > parser = pp.StringStart() + \ > pp.Literal('{').suppress() + \ > pp.delimitedList(withquotes | withoutquotes) + \ > pp.Literal('}').suppress() + \ > pp.StringEnd() > return parser.parseString(s).asList() > > which works beautifully, except on the input: "{}". How can I neatly > modify the parser to return an empty list in this case? > Yes, obviously, I could say > if s=='{}': return [] > It just seems like I'm missing some simple intrinsic way to get this > out of the parser. I am hoping to become more skillful in using the > wonderful pyparsing module! > > -- George Young > -- http://mail.python.org/mailman/listinfo/python-list
