pyparsing conditional parser

Question

I need to parse the following three lines:

Uptime is 1w2d
Last reset at 23:05:56
  Reason: reload

But last two lines are not always there, output could look like this prior to 1st reboot:

Uptime is 1w2d
Last reset

My parser looks like this:

parser = SkipTo(Literal('is'), include=True)('uptime') +
         delimitedList(Suppress(SkipTo(Literal('at'), include=True))'(reset)' +
             SkipTo(Literal(':'), include=true) +
             SkipTo(lineEnd)('reason'), combine=True)
         )

It works in first case with 3 lines, but doesnt work with second case.

Alessandro Suglia · Accepted Answer · 2014-08-11 15:53:24Z

2

I will use for the file that you've reported this syntax (supposing that the order is relevant):

from pyparsing import Literal, Word, alphanums, nums, alphas, Optional, delimitedList

def createParser():
    firstLine = Literal('Uptime is') + Word(alphanums)
    secLine = Literal('Last reset at') + delimitedList(Word(nums) + Literal(':') + Word(nums) + Literal(':') + Word(nums))
    thirdLine = Literal('Reason:') + Word(alphas)

    return firstLine + secLine + Optional(thirdLine)

if __name__ == '__main__':
     parser = createParser()
     firstText = """Uptime is 1w2d\n
     Last reset at 23:05:56\n
     Reason: reload"""

     print(parser.parseString(firstText))

Declaring a parsing element optional you are able to let the parser skip it when it is not present, without raising any errors.

answered Aug 11, 2014 at 15:53

Alessandro Suglia

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4 Comments

PaulMcG Over a year ago

+1, nice answer, Optional is definitely the way to go in solving this issue. I'm guessing that "Reason:" could reflect anything typed in by someone restarting the system, and could be more than one word in length. I would go with Literal("Reason:") + restOfLine instead, which will take in everything up to the next newline or the end of the input string if there are no more newlines.

dragon Over a year ago

!Allessandro looks good, I will test it. Thanks Paul, restOfLine is a nice one

Alessandro Suglia Over a year ago

If you think that it's a good code, consider to mark my comment as an answer. Thank you

dragon Over a year ago

Solution works, I did line by line parsing and then construct a parser using Optional

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