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decoder.py

00001 """
Implementation of JSONDecoder
"""
import re

from simplejson.scanner import Scanner, pattern

FLAGS = re.VERBOSE | re.MULTILINE | re.DOTALL

def _floatconstants():
    import struct
    import sys
    _BYTES = '7FF80000000000007FF0000000000000'.decode('hex')
    if sys.byteorder != 'big':
        _BYTES = _BYTES[:8][::-1] + _BYTES[8:][::-1]
    nan, inf = struct.unpack('dd', _BYTES)
    return nan, inf, -inf

NaN, PosInf, NegInf = _floatconstants()

def linecol(doc, pos):
    lineno = doc.count('\n', 0, pos) + 1
    if lineno == 1:
        colno = pos
    else:
        colno = pos - doc.rindex('\n', 0, pos)
    return lineno, colno

def errmsg(msg, doc, pos, end=None):
    lineno, colno = linecol(doc, pos)
    if end is None:
        return '%s: line %d column %d (char %d)' % (msg, lineno, colno, pos)
    endlineno, endcolno = linecol(doc, end)
    return '%s: line %d column %d - line %d column %d (char %d - %d)' % (
        msg, lineno, colno, endlineno, endcolno, pos, end)

_CONSTANTS = {
    '-Infinity': NegInf,
    'Infinity': PosInf,
    'NaN': NaN,
    'true': True,
    'false': False,
    'null': None,
}

def JSONConstant(match, context, c=_CONSTANTS):
    return c[match.group(0)], None
pattern('(-?Infinity|NaN|true|false|null)')(JSONConstant)

def JSONNumber(match, context):
    match = JSONNumber.regex.match(match.string, *match.span())
    integer, frac, exp = match.groups()
    if frac or exp:
        res = float(integer + (frac or '') + (exp or ''))
    else:
        res = int(integer)
    return res, None
pattern(r'(-?(?:0|[1-9]\d*))(\.\d+)?([eE][-+]?\d+)?')(JSONNumber)

STRINGCHUNK = re.compile(r'(.*?)(["\\])', FLAGS)
BACKSLASH = {
    '"': u'"', '\\': u'\\', '/': u'/',
    'b': u'\b', 'f': u'\f', 'n': u'\n', 'r': u'\r', 't': u'\t',
}

DEFAULT_ENCODING = "utf-8"

def scanstring(s, end, encoding=None, _b=BACKSLASH, _m=STRINGCHUNK.match):
    if encoding is None:
        encoding = DEFAULT_ENCODING
    chunks = []
    _append = chunks.append
    begin = end - 1
    while 1:
        chunk = _m(s, end)
        if chunk is None:
            raise ValueError(
                errmsg("Unterminated string starting at", s, begin))
        end = chunk.end()
        content, terminator = chunk.groups()
        if content:
            if not isinstance(content, unicode):
                content = unicode(content, encoding)
            _append(content)
        if terminator == '"':
            break
        try:
            esc = s[end]
        except IndexError:
            raise ValueError(
                errmsg("Unterminated string starting at", s, begin))
        if esc != 'u':
            try:
                m = _b[esc]
            except KeyError:
                raise ValueError(
                    errmsg("Invalid \\escape: %r" % (esc,), s, end))
            end += 1
        else:
            esc = s[end + 1:end + 5]
            try:
                m = unichr(int(esc, 16))
                if len(esc) != 4 or not esc.isalnum():
                    raise ValueError
            except ValueError:
                raise ValueError(errmsg("Invalid \\uXXXX escape", s, end))
            end += 5
        _append(m)
    return u''.join(chunks), end

def JSONString(match, context):
    encoding = getattr(context, 'encoding', None)
    return scanstring(match.string, match.end(), encoding)
pattern(r'"')(JSONString)

WHITESPACE = re.compile(r'\s*', FLAGS)

def JSONObject(match, context, _w=WHITESPACE.match):
    pairs = {}
    s = match.string
    end = _w(s, match.end()).end()
    nextchar = s[end:end + 1]
    # trivial empty object
    if nextchar == '}':
        return pairs, end + 1
    if nextchar != '"':
        raise ValueError(errmsg("Expecting property name", s, end))
    end += 1
    encoding = getattr(context, 'encoding', None)
    iterscan = JSONScanner.iterscan
    while True:
        key, end = scanstring(s, end, encoding)
        end = _w(s, end).end()
        if s[end:end + 1] != ':':
            raise ValueError(errmsg("Expecting : delimiter", s, end))
        end = _w(s, end + 1).end()
        try:
            value, end = iterscan(s, idx=end, context=context).next()
        except StopIteration:
            raise ValueError(errmsg("Expecting object", s, end))
        pairs[key] = value
        end = _w(s, end).end()
        nextchar = s[end:end + 1]
        end += 1
        if nextchar == '}':
            break
        if nextchar != ',':
            raise ValueError(errmsg("Expecting , delimiter", s, end - 1))
        end = _w(s, end).end()
        nextchar = s[end:end + 1]
        end += 1
        if nextchar != '"':
            raise ValueError(errmsg("Expecting property name", s, end - 1))
    object_hook = getattr(context, 'object_hook', None)
    if object_hook is not None:
        pairs = object_hook(pairs)
    return pairs, end
pattern(r'{')(JSONObject)
            
def JSONArray(match, context, _w=WHITESPACE.match):
    values = []
    s = match.string
    end = _w(s, match.end()).end()
    # look-ahead for trivial empty array
    nextchar = s[end:end + 1]
    if nextchar == ']':
        return values, end + 1
    iterscan = JSONScanner.iterscan
    while True:
        try:
            value, end = iterscan(s, idx=end, context=context).next()
        except StopIteration:
            raise ValueError(errmsg("Expecting object", s, end))
        values.append(value)
        end = _w(s, end).end()
        nextchar = s[end:end + 1]
        end += 1
        if nextchar == ']':
            break
        if nextchar != ',':
            raise ValueError(errmsg("Expecting , delimiter", s, end))
        end = _w(s, end).end()
    return values, end
pattern(r'\[')(JSONArray)
 
ANYTHING = [
    JSONObject,
    JSONArray,
    JSONString,
    JSONConstant,
    JSONNumber,
]

JSONScanner = Scanner(ANYTHING)

class JSONDecoder(object):
    """
    Simple JSON <http://json.org> decoder

    Performs the following translations in decoding:
    
    +---------------+-------------------+
    | JSON          | Python            |
    +===============+===================+
    | object        | dict              |
    +---------------+-------------------+
    | array         | list              |
    +---------------+-------------------+
    | string        | unicode           |
    +---------------+-------------------+
    | number (int)  | int, long         |
    +---------------+-------------------+
    | number (real) | float             |
    +---------------+-------------------+
    | true          | True              |
    +---------------+-------------------+
    | false         | False             |
    +---------------+-------------------+
    | null          | None              |
    +---------------+-------------------+

    It also understands ``NaN``, ``Infinity``, and ``-Infinity`` as
    their corresponding ``float`` values, which is outside the JSON spec.
    """

    _scanner = Scanner(ANYTHING)
    __all__ = ['__init__', 'decode', 'raw_decode']

    def __init__(self, encoding=None, object_hook=None):
        """
        ``encoding`` determines the encoding used to interpret any ``str``
        objects decoded by this instance (utf-8 by default).  It has no
        effect when decoding ``unicode`` objects.
        
        Note that currently only encodings that are a superset of ASCII work,
        strings of other encodings should be passed in as ``unicode``.

        ``object_hook``, if specified, will be called with the result
        of every JSON object decoded and its return value will be used in
        place of the given ``dict``.  This can be used to provide custom
        deserializations (e.g. to support JSON-RPC class hinting).
        """
        self.encoding = encoding
        self.object_hook = object_hook

    def decode(self, s, _w=WHITESPACE.match):
        """
        Return the Python representation of ``s`` (a ``str`` or ``unicode``
        instance containing a JSON document)
        """
        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
        end = _w(s, end).end()
        if end != len(s):
            raise ValueError(errmsg("Extra data", s, end, len(s)))
        return obj

    def raw_decode(self, s, **kw):
        """
        Decode a JSON document from ``s`` (a ``str`` or ``unicode`` beginning
        with a JSON document) and return a 2-tuple of the Python
        representation and the index in ``s`` where the document ended.

        This can be used to decode a JSON document from a string that may
        have extraneous data at the end.
        """
        kw.setdefault('context', self)
        try:
            obj, end = self._scanner.iterscan(s, **kw).next()
        except StopIteration:
            raise ValueError("No JSON object could be decoded")
        return obj, end

__all__ = ['JSONDecoder']

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