Optional??

[Ray Hooker]

I am trying to parse a line of from a Cisco config which has optional parameters.  For some reason, the following code does not work unless I put in the optional parameter.  It seems to read the next parameter after tag_server into nameif even if it is the literal "host".

#!/usr/local/bin/python
import sys
import string
import re
import os
import csv
import pyparsing

if __name__ == '__main__':
    # Now to test pyparsing
    from pyparsing import Literal, Word, alphanums, Optional, FollowedBy, ZeroOrMore, printables, MatchFirst
    propval = Word(printables)
    tag_server = propval.setResultsName("server_tag")
    nameif = propval.setResultsName("if_name")
    hostnm = propval.setResultsName("hostip")
    ifhost = nameif + Literal('host').suppress()
    HOST = Literal('host').suppress()
    aaa_server = Literal('aaa-server').suppress()+tag_server+ Optional(nameif)+HOST+hostnm
    #try:
    test = aaa_server.parseString("aaa-server tacacs+ host 192.168.5.12 test timeout 3")       
    #except:
    #    test = None
    if test:
        print test
        print test["if_name"]
    else:
        print "None found"

[Paul McGuire]

Ray -

What is the general format supposed to be for this line?  I'm guessing something like:

aaa-server <server-name> [<nameif>] host <ip-address> <other stuff on the rest of the line>

What you've tripped over is that pyparsing does not look ahead in the grammar for literals, the same way that regexp's do.  Since "host" is a word composed of printables, it looks to pyparsing like a perfectly valid nameif.  Since you don't want to accept "host" as this name, you should define nameif as:

nameif = (~HOST + propval).setResultsName("if_name")

(You'll have to move your declaration of HOST to the previous line or else Python will complain.)

-- Paul