source: branches/pyyaml3000/lib/yaml/reader.py @ 52

Revision 52, 7.7 KB checked in by xi, 9 years ago (diff)

Cleanup error messages.

Line 
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#   Marker(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
20from error import YAMLError, Marker
21
22import 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
27try:
28    codecs.utf_8_decode('', 'strict', False)
29    from codecs import utf_8_decode, utf_16_le_decode, utf_16_be_decode
30
31except 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
59class 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
80class 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.index = 0
104        self.line = 0
105        self.column = 0
106        if isinstance(data, unicode):
107            self.name = "<unicode string>"
108            self.check_printable(data)
109            self.buffer = data+u'\0'
110        elif isinstance(data, str):
111            self.name = "<string>"
112            self.raw_buffer = data
113            self.determine_encoding()
114        else:
115            self.stream = data
116            self.name = getattr(data, 'name', "<file>")
117            self.eof = False
118            self.raw_buffer = ''
119            self.determine_encoding()
120
121    def peek(self, index=0):
122        if self.pointer+index+1 >= len(self.buffer):
123            self.update(index+1)
124        return self.buffer[self.pointer+index]
125
126    def prefix(self, length=1):
127        if self.pointer+length >= len(self.buffer):
128            self.update(length)
129        return self.buffer[self.pointer:self.pointer+length]
130
131    def forward(self, length=1):
132        if self.pointer+length+1 >= len(self.buffer):
133            self.update(length+1)
134        for k in range(length):
135            ch = self.buffer[self.pointer]
136            self.pointer += 1
137            self.index += 1
138            if ch in u'\n\x85\u2028\u2029'  \
139                    or (ch == u'\r' and self.buffer[self.pointer+1] != u'\n'):
140                self.line += 1
141                self.column = 0
142            elif ch != u'\uFEFF':
143                self.column += 1
144
145    def get_marker(self):
146        if self.stream is None:
147            return Marker(self.name, self.line, self.column,
148                    self.buffer, self.pointer)
149        else:
150            return Marker(self.name, self.line, self.column, None, None)
151
152    def determine_encoding(self):
153        while not self.eof and len(self.raw_buffer) < 2:
154            self.update_raw()
155        if not isinstance(self.raw_buffer, unicode):
156            if self.raw_buffer.startswith(codecs.BOM_UTF16_LE):
157                self.raw_decode = utf_16_le_decode
158            elif self.raw_buffer.startswith(codecs.BOM_UTF16_BE):
159                self.raw_decode = utf_16_be_decode
160            else:
161                self.raw_decode = utf_8_decode
162        self.update(1)
163
164    NON_PRINTABLE = re.compile(u'[^\x09\x0A\x0D\x20-\x7E\x85\xA0-\uD7FF\uE000-\uFFFD]')
165    def check_printable(self, data):
166        match = self.NON_PRINTABLE.search(data)
167        if match:
168            character = match.group()
169            position = self.index+(len(self.buffer)-self.pointer)+match.start()
170            raise ReaderError(self.name, position, character,
171                    'unicode', "special characters are not allowed")
172
173    def update(self, length):
174        if self.raw_buffer is None:
175            return
176        self.buffer = self.buffer[self.pointer:]
177        self.pointer = 0
178        while len(self.buffer) < length:
179            if not self.eof:
180                self.update_raw()
181            if self.raw_decode is not None:
182                try:
183                    data, converted = self.raw_decode(self.raw_buffer,
184                            'strict', self.eof)
185                except UnicodeDecodeError, exc:
186                    character = exc.object[exc.start]
187                    if self.stream is not None:
188                        position = self.stream_pointer-len(self.raw_buffer)+exc.start
189                    else:
190                        position = exc.start
191                    raise ReaderError(self.name, position, character,
192                            exc.encoding, exc.reason)
193            else:
194                data = self.raw_buffer
195                converted = len(data)
196            self.check_printable(data)
197            self.buffer += data
198            self.raw_buffer = self.raw_buffer[converted:]
199            if self.eof:
200                self.buffer += u'\0'
201                self.raw_buffer = None
202                break
203
204    def update_raw(self, size=1024):
205        data = self.stream.read(size)
206        if data:
207            self.raw_buffer += data
208            self.stream_pointer += len(data)
209        else:
210            self.eof = True
211
212#try:
213#    import psyco
214#    psyco.bind(Reader)
215#except ImportError:
216#    pass
217
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