regular expression extracting groups

[clawsicus@gmail.com]

Hi list,

I'm trying to use regular expressions to help me quickly extract the
contents of messages that my application will receive. I have worked
out most of the regex but the last section of the message has me
stumped. This is mostly because I want to pull the content out into
regex groups that I can easily access later. I have a regex to extract
the key/value pairs but it ends up with only the contents of the last
key/value pair encountered.

An example of the section of the message that is troubling me appears
like this:

{
option=value
foo=bar
another=42
option=7
}

So it's basically a bunch of lines. Every line is terminated with a
'\n' character. The number of key/value fields changes depending on
the particular message. Also notice that there are two 'option' keys.
This is allowable and I need to cater for it.


A couple of example messages are:
xpl-stat\n{\nhop=1\ nsource=vendor-device.instance \ntarget=*\n}
\nhbeat.basic\n {\ninterval=10\ n}\n

xpl-stat\n{\nhop=1\ nsource=vendor-device.instance \ntarget=vendor-
device.instance \n}\nconfig.lis t\n{\nreconf=ne wconf\noption=i nterval
\noption=group[16]\noption=filter[16]\n}\n


As all messages follow the same pattern I'm hoping to develop a
generic regex, instead of one for each message kind - because there
are many, that can pull a message from a received packet.



The regex I came up with looks like this:
# This should match any xPL message

GROUP_MESSAGE_T YPE = 'message_type'
GROUP_HOP = 'hop'
GROUP_SOURCE = 'source'
GROUP_TARGET = 'target'
GROUP_SRC_VENDO R_ID = 'source_vendor_ id'
GROUP_SRC_DEVIC E_ID = 'source_device_ id'
GROUP_SRC_INSTA NCE_ID = 'source_instanc e_id'
GROUP_TGT_VENDO R_ID = 'target_vendor_ id'
GROUP_TGT_DEVIC E_ID = 'target_device_ id'
GROUP_TGT_INSTA NCE_ID = 'target_instanc e_id'
GROUP_IDENTIFIE R_TYPE = 'identifier_typ e'
GROUP_SCHEMA = 'schema'
GROUP_SCHEMA_CL ASS = 'schema_class'
GROUP_SCHEMA_TY PE = 'schema_type'
GROUP_OPTION_KE Y = 'key'
GROUP_OPTION_VA LUE = 'value'


XplMessageGroup sRe = r'''(?P<%s>xpl-(cmnd|stat|trig ))
\n # message type
\
{\n
#
hop=(?P<%s>[1-9]{1})
\n # hop
count
source=(?P<%s>( ?P<%s>[a-z0-9]{1,8})-(?P<%s>[a-z0-9]{1,8})\.(?P<
%s>[a-z0-9]{1,16}))\n # source identifier
target=(?P<%s>( \*|(?P<%s>[a-z0-9]{1,8})-(?P<%s>[a-z0-9]{1,8})\.(?P<
%s>[a-z0-9]{1,16})))\n # target identifier
\}
\n
#
(?P<%s>(?P<%s>[a-z0-9]{1,8})\.(?P<%s>[a-z0-9]{1,8}))\n
# schema
\
{\n
#
(?:(?P<%s>[a-z0-9\-]{1,16})=(?P<%s>[\x20-\x7E]{0,128})\n){1,6 4} #
key/value pairs
\}\n''' % (GROUP_MESSAGE_ TYPE,
GROUP_HOP,
GROUP_SOURCE,
GROUP_SRC_VENDO R_ID,
GROUP_SRC_DEVIC E_ID,
GROUP_SRC_INSTA NCE_ID,
GROUP_TARGET,
GROUP_TGT_VENDO R_ID,
GROUP_TGT_DEVIC E_ID,
GROUP_TGT_INSTA NCE_ID,
GROUP_SCHEMA,
GROUP_SCHEMA_CL ASS,
GROUP_SCHEMA_TY PE,
GROUP_OPTION_KE Y,
GROUP_OPTION_VA LUE)

XplMessageGroup s = re.compile(XplM essageGroupsRe, re.VERBOSE |
re.DOTALL)


If I pass the second example message through this regex the 'key'
group ends up containing 'option' and the 'value' group ends up
containing 'filter[16]' which are the last key/value pairs in that
message.

So the problem I have lies in the key/value regex extraction section.
It handles multiple occurrences of the pattern and writes the content
into the single key/value group hence I can't extract and access all
fields.

Is there some other way to do this which allows me to store all the
key/value pairs into the regex match object for later retrieval?
Perhaps using the standard unnamed number groups?

Thanks,
Chris

[Paul Hankin]

Re: regular expression extracting groups

On Aug 10, 2:30 pm, clawsi...@gmail .com wrote:

I'm trying to use regular expressions to help me quickly extract the
contents of messages that my application will receive.

Don't use regexps for parsing complex data; they're limited,
completely unreadable, and hugely difficult to debug. Your code is
well written, and you've already reached the limits of the power of
regexps, and it's difficult to read.

Have a look at pyparsing for a simple solution to your problem.

http://pyparsing.wikispaces.com/

--
Paul Hankin

[clawsicus@gmail.com]

Re: regular expression extracting groups

Thanks all for your responses, especially Paul McGuire for the
excellent example usage of pyparsing.
I'm off to check out pyparsing.

Thanks,
Chris