lib/yaml/reader.py

   1 # This module contains abstractions for the input stream. You don't have to
   2 # looks further, there are no pretty code.
   3 #
   4 # We define two classes here.
   5 #
   6 #   Mark(source, line, column)
   7 # It's just a record and its only use is producing nice error messages.
   8 # Parser does not use it for any other purposes.
   9 #
  10 #   Reader(source, data)
  11 # Reader determines the encoding of `data` and converts it to unicode.
  12 # Reader provides the following methods and attributes:
  13 #   reader.peek(length=1) - return the next `length` characters
  14 #   reader.forward(length=1) - move the current position to `length` characters.
  15 #   reader.index - the number of the current character.
  16 #   reader.line, stream.column - the line and the column of the current character.
  17
  18 __all__ = ['Reader', 'ReaderError']
  19
  20 from error import YAMLError, Mark
  21
  22 import codecs, re
  23
  24 # Unfortunately, codec functions in Python 2.3 does not support the `finish`
  25 # arguments, so we have to write our own wrappers.
  26
  27 try:
  28     codecs.utf_8_decode('', 'strict', False)
  29     from codecs import utf_8_decode, utf_16_le_decode, utf_16_be_decode
  30
  31 except TypeError:
  32
  33     def utf_16_le_decode(data, errors, finish=False):
  34         if not finish and len(data) % 2 == 1:
  35             data = data[:-1]
  36         return codecs.utf_16_le_decode(data, errors)
  37
  38     def utf_16_be_decode(data, errors, finish=False):
  39         if not finish and len(data) % 2 == 1:
  40             data = data[:-1]
  41         return codecs.utf_16_be_decode(data, errors)
  42
  43     def utf_8_decode(data, errors, finish=False):
  44         if not finish:
  45             # We are trying to remove a possible incomplete multibyte character
  46             # from the suffix of the data.
  47             # The first byte of a multi-byte sequence is in the range 0xc0 to 0xfd.
  48             # All further bytes are in the range 0x80 to 0xbf.
  49             # UTF-8 encoded UCS characters may be up to six bytes long.
  50             count = 0
  51             while count < 5 and count < len(data)   \
  52                     and '\x80' <= data[-count-1] <= '\xBF':
  53                 count -= 1
  54             if count < 5 and count < len(data)  \
  55                     and '\xC0' <= data[-count-1] <= '\xFD':
  56                 data = data[:-count-1]
  57         return codecs.utf_8_decode(data, errors)
  58
  59 class ReaderError(YAMLError):
  60
  61     def __init__(self, name, position, character, encoding, reason):
  62         self.name = name
  63         self.character = character
  64         self.position = position
  65         self.encoding = encoding
  66         self.reason = reason
  67
  68     def __str__(self):
  69         if isinstance(self.character, str):
  70             return "'%s' codec can't decode byte #x%02x: %s\n"  \
  71                     "  in \"%s\", position %d"    \
  72                     % (self.encoding, ord(self.character), self.reason,
  73                             self.name, self.position)
  74         else:
  75             return "unacceptable character #x%04x: %s\n"    \
  76                     "  in \"%s\", position %d"    \
  77                     % (ord(self.character), self.reason,
  78                             self.name, self.position)
  79
  80 class Reader:
  81     # Reader:
  82     # - determines the data encoding and converts it to unicode,
  83     # - checks if characters are in allowed range,
  84     # - adds '\0' to the end.
  85
  86     # Reader accepts
  87     #  - a `str` object,
  88     #  - a `unicode` object,
  89     #  - a file-like object with its `read` method returning `str`,
  90     #  - a file-like object with its `read` method returning `unicode`.
  91
  92     # Yeah, it's ugly and slow.
  93
  94     def __init__(self, data):
  95         self.name = None
  96         self.stream = None
  97         self.stream_pointer = 0
  98         self.eof = True
  99         self.buffer = u''
 100         self.pointer = 0
 101         self.raw_buffer = None
 102         self.raw_decode = None
 103         self.encoding = None
 104         self.index = 0
 105         self.line = 0
 106         self.column = 0
 107         if isinstance(data, unicode):
 108             self.name = "<unicode string>"
 109             self.check_printable(data)
 110             self.buffer = data+u'\0'
 111         elif isinstance(data, str):
 112             self.name = "<string>"
 113             self.raw_buffer = data
 114             self.determine_encoding()
 115         else:
 116             self.stream = data
 117             self.name = getattr(data, 'name', "<file>")
 118             self.eof = False
 119             self.raw_buffer = ''
 120             self.determine_encoding()
 121
 122     def peek(self, index=0):
 123         if self.pointer+index+1 >= len(self.buffer):
 124             self.update(index+1)
 125         return self.buffer[self.pointer+index]
 126
 127     def prefix(self, length=1):
 128         if self.pointer+length >= len(self.buffer):
 129             self.update(length)
 130         return self.buffer[self.pointer:self.pointer+length]
 131
 132     def forward(self, length=1):
 133         if self.pointer+length+1 >= len(self.buffer):
 134             self.update(length+1)
 135         for k in range(length):
 136             ch = self.buffer[self.pointer]
 137             self.pointer += 1
 138             self.index += 1
 139             if ch in u'\n\x85\u2028\u2029'  \
 140                     or (ch == u'\r' and self.buffer[self.pointer+1] != u'\n'):
 141                 self.line += 1
 142                 self.column = 0
 143             elif ch != u'\uFEFF':
 144                 self.column += 1
 145
 146     def get_mark(self):
 147         if self.stream is None:
 148             return Mark(self.name, self.index, self.line, self.column,
 149                     self.buffer, self.pointer)
 150         else:
 151             return Mark(self.name, self.index, self.line, self.column,
 152                     None, None)
 153
 154     def determine_encoding(self):
 155         while not self.eof and len(self.raw_buffer) < 2:
 156             self.update_raw()
 157         if not isinstance(self.raw_buffer, unicode):
 158             if self.raw_buffer.startswith(codecs.BOM_UTF16_LE):
 159                 self.raw_decode = utf_16_le_decode
 160                 self.encoding = 'utf-16-le'
 161             elif self.raw_buffer.startswith(codecs.BOM_UTF16_BE):
 162                 self.raw_decode = utf_16_be_decode
 163                 self.encoding = 'utf-16-be'
 164             else:
 165                 self.raw_decode = utf_8_decode
 166                 self.encoding = 'utf-8'
 167         self.update(1)
 168
 169     NON_PRINTABLE = re.compile(u'[^\x09\x0A\x0D\x20-\x7E\x85\xA0-\uD7FF\uE000-\uFFFD]')
 170     def check_printable(self, data):
 171         match = self.NON_PRINTABLE.search(data)
 172         if match:
 173             character = match.group()
 174             position = self.index+(len(self.buffer)-self.pointer)+match.start()
 175             raise ReaderError(self.name, position, character,
 176                     'unicode', "special characters are not allowed")
 177
 178     def update(self, length):
 179         if self.raw_buffer is None:
 180             return
 181         self.buffer = self.buffer[self.pointer:]
 182         self.pointer = 0
 183         while len(self.buffer) < length:
 184             if not self.eof:
 185                 self.update_raw()
 186             if self.raw_decode is not None:
 187                 try:
 188                     data, converted = self.raw_decode(self.raw_buffer,
 189                             'strict', self.eof)
 190                 except UnicodeDecodeError, exc:
 191                     character = exc.object[exc.start]
 192                     if self.stream is not None:
 193                         position = self.stream_pointer-len(self.raw_buffer)+exc.start
 194                     else:
 195                         position = exc.start
 196                     raise ReaderError(self.name, position, character,
 197                             exc.encoding, exc.reason)
 198             else:
 199                 data = self.raw_buffer
 200                 converted = len(data)
 201             self.check_printable(data)
 202             self.buffer += data
 203             self.raw_buffer = self.raw_buffer[converted:]
 204             if self.eof:
 205                 self.buffer += u'\0'
 206                 self.raw_buffer = None
 207                 break
 208
 209     def update_raw(self, size=1024):
 210         data = self.stream.read(size)
 211         if data:
 212             self.raw_buffer += data
 213             self.stream_pointer += len(data)
 214         else:
 215             self.eof = True
 216
 217 #try:
 218 #    import psyco
 219 #    psyco.bind(Reader)
 220 #except ImportError:
 221 #    pass
 222