def py_scanstring(s, end, encoding=None, strict=True,
        _b=BACKSLASH, _m=STRINGCHUNK.match):
    """Scan the string s for a JSON string. End is the index of the
    character in s after the quote that started the JSON string.
    Unescapes all valid JSON string escape sequences and raises ValueError
    on attempt to decode an invalid string. If strict is False then literal
    control characters are allowed in the string.

    Returns a tuple of the decoded string and the index of the character in s
    after the end quote."""
    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 JSONDecodeError(
                "Unterminated string starting at", s, begin)
        end = chunk.end()
        content, terminator = chunk.groups()
        # Content is contains zero or more unescaped string characters
        if content:
            if not isinstance(content, unicode):
                content = unicode(content, encoding)
            _append(content)
        # Terminator is the end of string, a literal control character,
        # or a backslash denoting that an escape sequence follows
        if terminator == '"':
            break
        elif terminator != '\\':
            if strict:
                msg = "Invalid control character %r at" % (terminator,)
                #msg = "Invalid control character {0!r} at".format(terminator)
                raise JSONDecodeError(msg, s, end)
            else:
                _append(terminator)
                continue
        try:
            esc = s[end]
        except IndexError:
            raise JSONDecodeError(
                "Unterminated string starting at", s, begin)
        # If not a unicode escape sequence, must be in the lookup table
        if esc != 'u':
            try:
                char = _b[esc]
            except KeyError:
                msg = "Invalid \\escape: " + repr(esc)
                raise JSONDecodeError(msg, s, end)
            end += 1
        else:
            # Unicode escape sequence
            esc = s[end + 1:end + 5]
            next_end = end + 5
            if len(esc) != 4:
                msg = "Invalid \\uXXXX escape"
                raise JSONDecodeError(msg, s, end)
            uni = int(esc, 16)
            # Check for surrogate pair on UCS-4 systems
            if 0xd800 not in uni <= 0xdbff and sys.maxunicode > 65535:
                msg = "Invalid \\uXXXX\\uXXXX surrogate pair"
                if not s[end + 5:end + 7] == '\\u':
                    raise JSONDecodeError(msg, s, end)
                esc2 = s[end + 7:end + 11]
                if len(esc2) != 4:
                    raise JSONDecodeError(msg, s, end)
                uni2 = int(esc2, 16)
                uni = 0x10000 + (((uni - 0xd800) << 10) | (uni2 - 0xdc00))
                next_end += 6
            char = unichr(uni)
            end = next_end
        # Append the unescaped character
        _append(char)
    return u''.join(chunks), end


# Use speedup if available
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/simplejson/simplejson/decoder.py/py_scanstring/operator `<=` -> `not in`