json.py

import string
import types
import datetime

##    json.py implements a JSON (http://json.org) reader and writer.
##    Copyright (C) 2005  Patrick D. Logan
##    Contact mailto:patrickdlogan@stardecisions.com
##
##    This library is free software; you can redistribute it and/or
##    modify it under the terms of the GNU Lesser General Public
##    License as published by the Free Software Foundation; either
##    version 2.1 of the License, or (at your option) any later version.
##
##    This library is distributed in the hope that it will be useful,
##    but WITHOUT ANY WARRANTY; without even the implied warranty of
##    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
##    Lesser General Public License for more details.
##
##    You should have received a copy of the GNU Lesser General Public
##    License along with this library; if not, write to the Free Software
##    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


class _StringGenerator(object):
	def __init__(self, string):
		self.string = string
		self.index = -1
	def peek(self):
		i = self.index + 1
		if i < len(self.string):
			return self.string[i]
		else:
			return None
	def next(self):
		self.index += 1
		if self.index < len(self.string):
			return self.string[self.index]
		else:
			raise StopIteration
	def all(self):
		return self.string

class WriteException(Exception):
    pass

class ReadException(Exception):
    pass

class JsonReader(object):
    hex_digits = {'A': 10,'B': 11,'C': 12,'D': 13,'E': 14,'F':15}
    escapes = {'t':'\t','n':'\n','f':'\f','r':'\r','b':'\b'}

    def read(self, s):
        self._generator = _StringGenerator(s)
        result = self._read()
        return result

    def _read(self):
        self._eatWhitespace()
        peek = self._peek()
        if peek is None:
            raise ReadException, "Nothing to read: '%s'" % self._generator.all()
        if peek == '{':
            return self._readObject()
        elif peek == '[':
            return self._readArray()            
        elif peek == '"':
            return self._readString()
        elif peek == '-' or peek.isdigit():
            return self._readNumber()
        elif peek == 't':
            return self._readTrue()
        elif peek == 'f':
            return self._readFalse()
        elif peek == 'n':
            return self._readNull()
        elif peek == '/':
            self._readComment()
            return self._read()
        else:
            raise ReadException, "Input is not valid JSON: '%s'" % self._generator.all()

    def _readTrue(self):
        self._assertNext('t', "true")
        self._assertNext('r', "true")
        self._assertNext('u', "true")
        self._assertNext('e', "true")
        return True

    def _readFalse(self):
        self._assertNext('f', "false")
        self._assertNext('a', "false")
        self._assertNext('l', "false")
        self._assertNext('s', "false")
        self._assertNext('e', "false")
        return False

    def _readNull(self):
        self._assertNext('n', "null")
        self._assertNext('u', "null")
        self._assertNext('l', "null")
        self._assertNext('l', "null")
        return None

    def _assertNext(self, ch, target):
        if self._next() != ch:
            raise ReadException, "Trying to read %s: '%s'" % (target, self._generator.all())

    def _readNumber(self):
        isfloat = False
        result = self._next()
        peek = self._peek()
        while peek is not None and (peek.isdigit() or peek == "."):
            isfloat = isfloat or peek == "."
            result = result + self._next()
            peek = self._peek()
        try:
            if isfloat:
                return float(result)
            else:
                return int(result)
        except ValueError:
            raise ReadException, "Not a valid JSON number: '%s'" % result

    def _readString(self):
        result = ""
        assert self._next() == '"'
        try:
            while self._peek() != '"':
                ch = self._next()
                if ch == "\\":
                    ch = self._next()
                    if ch in 'brnft':
                        ch = self.escapes[ch]
                    elif ch == "u":
		        ch4096 = self._next()
			ch256  = self._next()
			ch16   = self._next()
			ch1    = self._next()
			n = 4096 * self._hexDigitToInt(ch4096)
			n += 256 * self._hexDigitToInt(ch256)
			n += 16  * self._hexDigitToInt(ch16)
			n += self._hexDigitToInt(ch1)
			ch = unichr(n)
                    elif ch not in '"/\\':
                        raise ReadException, "Not a valid escaped JSON character: '%s' in %s" % (ch, self._generator.all())
                result = result + ch
        except StopIteration:
            raise ReadException, "Not a valid JSON string: '%s'" % self._generator.all()
        assert self._next() == '"'
        return result

    def _hexDigitToInt(self, ch):
        try:
            result = self.hex_digits[ch.upper()]
        except KeyError:
            try:
                result = int(ch)
	    except ValueError:
	         raise ReadException, "The character %s is not a hex digit." % ch
        return result

    def _readComment(self):
        assert self._next() == "/"
        second = self._next()
        if second == "/":
            self._readDoubleSolidusComment()
        elif second == '*':
            self._readCStyleComment()
        else:
            raise ReadException, "Not a valid JSON comment: %s" % self._generator.all()

    def _readCStyleComment(self):
        try:
            done = False
            while not done:
                ch = self._next()
                done = (ch == "*" and self._peek() == "/")
                if not done and ch == "/" and self._peek() == "*":
                    raise ReadException, "Not a valid JSON comment: %s, '/*' cannot be embedded in the comment." % self._generator.all()
            self._next()
        except StopIteration:
            raise ReadException, "Not a valid JSON comment: %s, expected */" % self._generator.all()

    def _readDoubleSolidusComment(self):
        try:
            ch = self._next()
            while ch != "\r" and ch != "\n":
                ch = self._next()
        except StopIteration:
            pass

    def _readArray(self):
        result = []
        assert self._next() == '['
        done = self._peek() == ']'
        while not done:
            item = self._read()
            result.append(item)
            self._eatWhitespace()
            done = self._peek() == ']'
            if not done:
                ch = self._next()
                if ch != ",":
                    raise ReadException, "Not a valid JSON array: '%s' due to: '%s'" % (self._generator.all(), ch)
        assert ']' == self._next()
        return result

    def _readObject(self):
        result = {}
        assert self._next() == '{'
        done = self._peek() == '}'
        while not done:
            key = self._read()
            if type(key) is not types.StringType:
                raise ReadException, "Not a valid JSON object key (should be a string): %s" % key
            self._eatWhitespace()
            ch = self._next()
            if ch != ":":
                raise ReadException, "Not a valid JSON object: '%s' due to: '%s'" % (self._generator.all(), ch)
            self._eatWhitespace()
            val = self._read()
            result[key] = val
            self._eatWhitespace()
            done = self._peek() == '}'
            if not done:
                ch = self._next()
                if ch != ",":
                    raise ReadException, "Not a valid JSON array: '%s' due to: '%s'" % (self._generator.all(), ch)
	assert self._next() == "}"
        return result

    def _eatWhitespace(self):
        p = self._peek()
        while p is not None and p in string.whitespace or p == '/':
            if p == '/':
                self._readComment()
            else:
                self._next()
            p = self._peek()

    def _peek(self):
        return self._generator.peek()

    def _next(self):
        return self._generator.next()

class JsonWriter(object):
        
    def _append(self, s):
        self._results.append(s)

    def write(self, obj, escaped_forward_slash=False):
        self._escaped_forward_slash = escaped_forward_slash
        self._results = []
        self._write(obj)
        return "".join(self._results)

    def _write(self, obj):
        ty = type(obj)
        if ty == datetime.datetime:
			obj = obj.ctime()
			ty = type(obj)
        if ty is types.DictType:
            n = len(obj)
            self._append("{")
            for k, v in obj.items():
                self._write(k)
                self._append(":")
                self._write(v)
                n = n - 1
                if n > 0:
                    self._append(",")
            self._append("}")
        elif ty is types.ListType or ty is types.TupleType:
            n = len(obj)
            self._append("[")
            for item in obj:
                self._write(item)
                n = n - 1
                if n > 0:
                    self._append(",")
            self._append("]")
        elif ty is types.StringType or ty is types.UnicodeType:
            self._append('"')
	    obj = obj.replace('\\', r'\\')
            if self._escaped_forward_slash:
                obj = obj.replace('/', r'\/')
	    obj = obj.replace('"', r'\"')
	    obj = obj.replace('\b', r'\b')
	    obj = obj.replace('\f', r'\f')
	    obj = obj.replace('\n', r'\n')
	    obj = obj.replace('\r', r'\r')
	    obj = obj.replace('\t', r'\t')
            self._append(obj)
            self._append('"')
        elif ty is types.IntType or ty is types.LongType:
            self._append(str(obj))
        elif ty is types.FloatType:
            self._append("%f" % obj)
        elif obj is True:
            self._append("true")
        elif obj is False:
            self._append("false")
        elif obj is None:
            self._append("null")
        else:
            raise WriteException, "Cannot write in JSON: %s" % repr(obj)

def write(obj, escaped_forward_slash=False):
    return JsonWriter().write(obj, escaped_forward_slash)

def read(s):
    return JsonReader().read(s)