[Tutor] Regular Expression help - parsing AppleScript Lists as Strings

[Andrew Wu]

Hi,

I'm writing utilities to handle return values from AppleScript in python and
one of the steps is recognizing when a returned value from an AppleScript
execution (via popen and osascript) represents a list (in AppleScript) or
not.  For the most part I think I have the correct matching pattern, but I
am hung up on one of the sample strings I was using to test it - AppleScript
allows for one level of nested lists (I believe) and I get tripped up with
attempting to match lists with nested lists.

My second question is, once I have a pattern matching correctly, I need to
convert the AppleScript list into a Python list - I've read a bit about the
findall() method of the re module and was wondering if that would work in
this instance (there's also split() but I've been having issues with that,
probably b/c my pattern matching isn't correct).


Thank you!

Andrew

(source code below)



#!/usr/bin/env python
# Sample script to test if a string represented an AppleScript List or not

import re
import os

def IsASList(thestr=''):
   # AppleScript lists are bracked by curly braces with items separate by
commas
   # Each item is an alphanumeric label(?) or a string enclosed by
   # double quotes or a list itself
   # e.g. {2, True, "hello"}
   #
   # They differ from AppleScript records in that AS records have a key and
value:
   # {name: "Buffy", field: "Slaying", job: true, age: 21}
   #
   # Now the question is how to make the distinction?

   pattern = '''
      ^{    # Must start with a curly brace
      (
      \s*?     # Group to repeat; clear the whitespace after commas first
      (       # Start of group of alternating match possibilities
      ".+?"   # Match a string
      | \d+?     # Match a number
      | true|false  # Match 'true' or 'false' label
      )       # End of group of alternating match possibilities
      ,?)*     # Items are comma-delimited, except for the last item
      }$    # Must end with a closing curly brace
   '''

   pattern2 = '''
      (
      \s*?     # Group to repeat; clear the whitespace after commas first
      (       # Start of group of alternating match possibilities
      ".+?"   # Match a string
      | \d+?     # Match a number
      | true|false  # Match 'true' or 'false' label
      )       # End of group of alternating match possibilities
      ,?)*     # Items are comma-delimited, except for the last item
   '''

   pattern3 = '''
      ^{
      (
      %s
      | {%s}   # Possible to have 1 level of nested lists
      ,?)*     # Items are comma-delimited, except for the last item
      }$
   ''' % (pattern2, pattern2)

   regex = re.compile(pattern3, re.VERBOSE)
   result = regex.match(thestr)

#   print 'Result: ',
#   try:
#      print result.groups()
#   except AttributeError:
#      pass

   if result:
      return True
   else:
      return False


# main()

sample_strs = [
   '{}',      # Empty list
   '{a}',     # Should not match
   '{a, b, c}', # Should not match
   '{"hello"}',
   '{"hello", "kitty"}',
   '{true}',
   '{false}',
   '{true, false}',
   '{9}',
   '{9,10, 11}',
   '{93214, true, false, "hello", "kitty"}',
   '{{1, 2, 3}}',  # This matches
   '{{1, 2, "cat"}, 1}',  # This matches

    # These don't match:
   '{{1,2,3},1,{4,5,6},2}',
   '{1, {2, 3, 4}, 3}',
   '{{1, 2, 3}, {4, 5, 6}, 1}',
   '{1, {1, 2, 3}}',  # Should match but doesn't
   '{93214, true, false, "hello", "kitty", {1, 2, 3}}',  # Should match but
doesn't
   '{label: "hello", value: false, num: 2}',  # AppleScript dictionary -
should not match
]

for sample in sample_strs:
   print 'Is AppleScript List:  %s;   String:  %s' % (str(IsASList(sample)),
sample)
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