input-validation & string conversion

I have a script, which take input from the user and I want to validate the input first then convert the user-input to a predefined format. The input should be like this:

my_script -c 'formatDate(%d/%m) == 23/5 && userName == John Dee && status == c

At the moment I'm dealing with formatDate() bit only. The main rules are:

• The format string for year,month,day can come in any order
• if m [or y or d] is missing that will be added using current_month; same for others
• the same delimiter must be used for the format strings and the values
• the keys and values must be separated by ==
• the different constraint must be separated by &&
• single or multiple constraints are allowed

So, for the given example, it should return 20110523 as a valid constraint. After a bit of work, this is what I come up with, which is pretty much working:

#!/usr/bin/env python
#
import sys, re
from time import localtime, strftime

theDy = strftime('%d', localtime())
theMn = strftime('%m', localtime())
theYr = strftime('%Y', localtime())

def main(arg):

    print "input string: %s" % arg
    arg = "".join(arg.split()).lower()

    if arg.startswith('=') or re.search('===', arg) or "==" not in arg:
       sys.exit("Invalid query string!")
    else: my_arg = arg.split('&&')

    c_dict = {}

    for ix in range(len(my_arg)):
       LL = my_arg[ix].split('==')
       #LL = dict(zip(LL[:-1:2], LL[1::2]))

       # don't add duplicate key
       if not c_dict.has_key(LL[0]):
          c_dict[LL[0]] = LL[1]

       for k,v in sorted(c_dict.items()):
          if k.startswith('formatdate') :
             ymd = re.sub(r'[(,)]', ' ', k).replace('formatdate','')
             ymd = (str(ymd).strip()).split('/')
             if len(ymd) <= 3 and len(ymd) == len(v.split('/')):
                d_dict = dict(zip(ymd, v.split('/')))

                if not d_dict.has_key('%y'):
                   d_dict['%y'] = theYr
                if not d_dict.has_key('%m'):
                   d_dict['%m'] = theMn
                if not d_dict.has_key('%d'):
                   d_dict['%d'] = theDy

             else: sys.exit('date format mismatched!!')

             Y = d_dict['%y'];

             if d_dict['%m'].isdigit() and int(d_dict['%m']) <=12:
                M = d_dict['%m'].zfill(2)
             else: sys.exit("\"Month\" is not numeric or out of range.\nExiting...\n")

             if d_dict['%d'].isdigit() and int(d_dict['%d']) <=31:
                D = d_dict['%d'].zfill(2)
             else: sys.exit("\"Day\" is not numeric or out of range.\nExiting...\n")

             # next line needed for future use  
             fmtFile = re.compile('%s%s%s' % (Y,M,D))
             print "file_name is: %s" % Y+M+D

if __name__ == "__main__":
    main('formatDate(%d/%m)== 23/5')

My questions are:

• Am I making it unnecessarily complected or expensive? Is there any easier way?
• How to identify which "delimiter" user has used [as opposed to using a fixed one]?

Thanks for your time. Cheers!!