Optional??

Ray Hooker
2005-01-18
2013-05-14
  • Ray Hooker

    Ray Hooker - 2005-01-18

    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

      Paul McGuire - 2005-01-27

      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

       

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