Minimal JSON object parser

jsonP.py

import re

KEY_REGEX = '^[,]?["][a-zA-Z_][\w-]*["]$'
VALUE_REGEX = '^["].*["][,]?$'

CURLY_PAIR = ('{', '}')
SQ_PAIR = ('[', ']')

class JSONException(Exception):
   def __init__(self, value):
       self.value = value
   def __str__(self):
       return str(self.value)

class JSON(object):
   def __init__(self, f):
       self.contents = ''
       if isinstance(f, file):
          self.contents = f.readlines()[0]
          f.close()
       elif isinstance(f, str):
          with open(f, 'rb') as fp:
             self.contents = fp.readlines()[0]
       else:
          raise JSONException("Input file not valid, only str and file types are accepted")
       self.representation = self.parse(self.contents,{})

   def preProcess(self, s):
       last_c = None
       first_c = None
       for i,c in enumerate(s):
           if c == ' ':
              pass
           else:
              if first_c is None:
                 first_c = i
              else:
                 last_c = i
       if first_c != None and last_c is None:
          return s[first_c]
       elif first_c is None and last_c is None:
          return ''
       return s[first_c:last_c+1]

   def fileSyntax(self, content):
       squareLevel = 0
       curlyLevel = 0
       for i in content:
           if i == '{':
              curlyLevel += 1
           elif i == '}':
              curlyLevel -= 1
           if i == '[':
              squareLevel += 1
           elif i == ']':
              squareLevel -= 1
       return squareLevel == 0 and curlyLevel == 0

   def findBrace(self, content, pos, symPair):
       bracketLevel = 1
       imLevel = -1
       for i in range(pos+1, len(content)):
           if content[i] == symPair[0]:
              bracketLevel += 1
           elif content[i] == symPair[1]:
              bracketLevel -= 1
           if bracketLevel == 0:
              imLevel = i
              break
       return imLevel

   def splitByComma(self, content):
       level = 0
       elements = []
       accum = ''
       next = False
       for c in content:
           if c == '{' or c == '[':
              level += 1
           elif c == ']' or c == '}':
              level -= 1
           if c == ',' and level == 0:
              elements.append(accum)
              next = True
           accum += c
           if next:
              accum = ''
              next = False
       if level == 0:
          elements.append(accum)
       return elements

   def parse(self, content, d = {}):
       content = self.preProcess(content)
       if self.fileSyntax(content):
          accum = ''
          accumCopy = ''
          key = None
          value = None
          curlyLevel = 0
          pos = 0
          while pos < len(content):
            if content[pos] == '{':
               if d is None:
                  d = {}
               curlyLevel += 1
               accum = ''
               pos += 1
            accum += content[pos]
            if accum[-1] == ':' and key is None:
               #print accum
               #print re.findall(KEY_REGEX, accum[:-1])
               if len(re.findall(KEY_REGEX, accum[:-1])) == 1:
                  key = accum[:-1]
                  accumCopy = str(accum)
                  accum = ''
                  if key[0] == ',':
                     key = key[1:]
                  if content[pos+1] == '{':
                     levelEnd = self.findBrace(content, pos+1, CURLY_PAIR)
                     print content[pos+1:levelEnd+1]
                     value = self.parse(content[pos+1:levelEnd+1],{})
                     d[key] = value
                     key = None
                     value = None
                     pos = levelEnd
                  elif content[pos+1] == '[':
                     levelEnd = self.findBrace(content, pos+1, SQ_PAIR)
                     array = content[pos+2:levelEnd]
                     #elements = array.split(',')
                     print array
                     elements = self.splitByComma(array)
                     print elements
                     value = map(lambda e: self.parse(e,{}), elements)
                     d[key] = value
                     key = None
                     value = None
                     pos = levelEnd
               else:
                  raise JSONException("The file syntax is malformed: %s" % (accum))
            if len(accum) > 0 and accum[-1] == ',' and key is not None:
               if len(re.findall(VALUE_REGEX, accum[:-1])) == 1:
                  value = accum[:-1]
                  d[key] = value
                  key = None
                  value = None
                  accum = ''
               else:
                  raise JSONException("The file syntax is malformed: %s" % (accum))
            elif len(accum) > 0 and accum[-1] == '}' and key is not None:
               if len(re.findall(VALUE_REGEX, accum[:-1])) == 1:
                  value = accum[:-1]
                  d[key] = value
                  key = None
                  value = None
                  accum = ''
               else:
                  raise JSONException("The file syntax is malformed: %s" % (accum))
            pos += 1
       else:
          raise JSONException("The file syntax is malformed %s" % (content))
       return d