source: pyyaml/trunk/lib/yaml/scanner.py @ 354

Revision 354, 51.4 KB checked in by xi, 5 years ago (diff)

Fixed a problem with a scanner error not detected when no line break at the end of the stream.

Line 
1
2# Scanner produces tokens of the following types:
3# STREAM-START
4# STREAM-END
5# DIRECTIVE(name, value)
6# DOCUMENT-START
7# DOCUMENT-END
8# BLOCK-SEQUENCE-START
9# BLOCK-MAPPING-START
10# BLOCK-END
11# FLOW-SEQUENCE-START
12# FLOW-MAPPING-START
13# FLOW-SEQUENCE-END
14# FLOW-MAPPING-END
15# BLOCK-ENTRY
16# FLOW-ENTRY
17# KEY
18# VALUE
19# ALIAS(value)
20# ANCHOR(value)
21# TAG(value)
22# SCALAR(value, plain, style)
23#
24# Read comments in the Scanner code for more details.
25#
26
27__all__ = ['Scanner', 'ScannerError']
28
29from error import MarkedYAMLError
30from tokens import *
31
32class ScannerError(MarkedYAMLError):
33    pass
34
35class SimpleKey(object):
36    # See below simple keys treatment.
37
38    def __init__(self, token_number, required, index, line, column, mark):
39        self.token_number = token_number
40        self.required = required
41        self.index = index
42        self.line = line
43        self.column = column
44        self.mark = mark
45
46class Scanner(object):
47
48    def __init__(self):
49        """Initialize the scanner."""
50        # It is assumed that Scanner and Reader will have a common descendant.
51        # Reader do the dirty work of checking for BOM and converting the
52        # input data to Unicode. It also adds NUL to the end.
53        #
54        # Reader supports the following methods
55        #   self.peek(i=0)       # peek the next i-th character
56        #   self.prefix(l=1)     # peek the next l characters
57        #   self.forward(l=1)    # read the next l characters and move the pointer.
58
59        # Had we reached the end of the stream?
60        self.done = False
61
62        # The number of unclosed '{' and '['. `flow_level == 0` means block
63        # context.
64        self.flow_level = 0
65
66        # List of processed tokens that are not yet emitted.
67        self.tokens = []
68
69        # Add the STREAM-START token.
70        self.fetch_stream_start()
71
72        # Number of tokens that were emitted through the `get_token` method.
73        self.tokens_taken = 0
74
75        # The current indentation level.
76        self.indent = -1
77
78        # Past indentation levels.
79        self.indents = []
80
81        # Variables related to simple keys treatment.
82
83        # A simple key is a key that is not denoted by the '?' indicator.
84        # Example of simple keys:
85        #   ---
86        #   block simple key: value
87        #   ? not a simple key:
88        #   : { flow simple key: value }
89        # We emit the KEY token before all keys, so when we find a potential
90        # simple key, we try to locate the corresponding ':' indicator.
91        # Simple keys should be limited to a single line and 1024 characters.
92
93        # Can a simple key start at the current position? A simple key may
94        # start:
95        # - at the beginning of the line, not counting indentation spaces
96        #       (in block context),
97        # - after '{', '[', ',' (in the flow context),
98        # - after '?', ':', '-' (in the block context).
99        # In the block context, this flag also signifies if a block collection
100        # may start at the current position.
101        self.allow_simple_key = True
102
103        # Keep track of possible simple keys. This is a dictionary. The key
104        # is `flow_level`; there can be no more that one possible simple key
105        # for each level. The value is a SimpleKey record:
106        #   (token_number, required, index, line, column, mark)
107        # A simple key may start with ALIAS, ANCHOR, TAG, SCALAR(flow),
108        # '[', or '{' tokens.
109        self.possible_simple_keys = {}
110
111    # Public methods.
112
113    def check_token(self, *choices):
114        # Check if the next token is one of the given types.
115        while self.need_more_tokens():
116            self.fetch_more_tokens()
117        if self.tokens:
118            if not choices:
119                return True
120            for choice in choices:
121                if isinstance(self.tokens[0], choice):
122                    return True
123        return False
124
125    def peek_token(self):
126        # Return the next token, but do not delete if from the queue.
127        while self.need_more_tokens():
128            self.fetch_more_tokens()
129        if self.tokens:
130            return self.tokens[0]
131
132    def get_token(self):
133        # Return the next token.
134        while self.need_more_tokens():
135            self.fetch_more_tokens()
136        if self.tokens:
137            self.tokens_taken += 1
138            return self.tokens.pop(0)
139
140    # Private methods.
141
142    def need_more_tokens(self):
143        if self.done:
144            return False
145        if not self.tokens:
146            return True
147        # The current token may be a potential simple key, so we
148        # need to look further.
149        self.stale_possible_simple_keys()
150        if self.next_possible_simple_key() == self.tokens_taken:
151            return True
152
153    def fetch_more_tokens(self):
154
155        # Eat whitespaces and comments until we reach the next token.
156        self.scan_to_next_token()
157
158        # Remove obsolete possible simple keys.
159        self.stale_possible_simple_keys()
160
161        # Compare the current indentation and column. It may add some tokens
162        # and decrease the current indentation level.
163        self.unwind_indent(self.column)
164
165        # Peek the next character.
166        ch = self.peek()
167
168        # Is it the end of stream?
169        if ch == u'\0':
170            return self.fetch_stream_end()
171
172        # Is it a directive?
173        if ch == u'%' and self.check_directive():
174            return self.fetch_directive()
175
176        # Is it the document start?
177        if ch == u'-' and self.check_document_start():
178            return self.fetch_document_start()
179
180        # Is it the document end?
181        if ch == u'.' and self.check_document_end():
182            return self.fetch_document_end()
183
184        # TODO: support for BOM within a stream.
185        #if ch == u'\uFEFF':
186        #    return self.fetch_bom()    <-- issue BOMToken
187
188        # Note: the order of the following checks is NOT significant.
189
190        # Is it the flow sequence start indicator?
191        if ch == u'[':
192            return self.fetch_flow_sequence_start()
193
194        # Is it the flow mapping start indicator?
195        if ch == u'{':
196            return self.fetch_flow_mapping_start()
197
198        # Is it the flow sequence end indicator?
199        if ch == u']':
200            return self.fetch_flow_sequence_end()
201
202        # Is it the flow mapping end indicator?
203        if ch == u'}':
204            return self.fetch_flow_mapping_end()
205
206        # Is it the flow entry indicator?
207        if ch == u',':
208            return self.fetch_flow_entry()
209
210        # Is it the block entry indicator?
211        if ch == u'-' and self.check_block_entry():
212            return self.fetch_block_entry()
213
214        # Is it the key indicator?
215        if ch == u'?' and self.check_key():
216            return self.fetch_key()
217
218        # Is it the value indicator?
219        if ch == u':' and self.check_value():
220            return self.fetch_value()
221
222        # Is it an alias?
223        if ch == u'*':
224            return self.fetch_alias()
225
226        # Is it an anchor?
227        if ch == u'&':
228            return self.fetch_anchor()
229
230        # Is it a tag?
231        if ch == u'!':
232            return self.fetch_tag()
233
234        # Is it a literal scalar?
235        if ch == u'|' and not self.flow_level:
236            return self.fetch_literal()
237
238        # Is it a folded scalar?
239        if ch == u'>' and not self.flow_level:
240            return self.fetch_folded()
241
242        # Is it a single quoted scalar?
243        if ch == u'\'':
244            return self.fetch_single()
245
246        # Is it a double quoted scalar?
247        if ch == u'\"':
248            return self.fetch_double()
249
250        # It must be a plain scalar then.
251        if self.check_plain():
252            return self.fetch_plain()
253
254        # No? It's an error. Let's produce a nice error message.
255        raise ScannerError("while scanning for the next token", None,
256                "found character %r that cannot start any token"
257                % ch.encode('utf-8'), self.get_mark())
258
259    # Simple keys treatment.
260
261    def next_possible_simple_key(self):
262        # Return the number of the nearest possible simple key. Actually we
263        # don't need to loop through the whole dictionary. We may replace it
264        # with the following code:
265        #   if not self.possible_simple_keys:
266        #       return None
267        #   return self.possible_simple_keys[
268        #           min(self.possible_simple_keys.keys())].token_number
269        min_token_number = None
270        for level in self.possible_simple_keys:
271            key = self.possible_simple_keys[level]
272            if min_token_number is None or key.token_number < min_token_number:
273                min_token_number = key.token_number
274        return min_token_number
275
276    def stale_possible_simple_keys(self):
277        # Remove entries that are no longer possible simple keys. According to
278        # the YAML specification, simple keys
279        # - should be limited to a single line,
280        # - should be no longer than 1024 characters.
281        # Disabling this procedure will allow simple keys of any length and
282        # height (may cause problems if indentation is broken though).
283        for level in self.possible_simple_keys.keys():
284            key = self.possible_simple_keys[level]
285            if key.line != self.line  \
286                    or self.index-key.index > 1024:
287                if key.required:
288                    raise ScannerError("while scanning a simple key", key.mark,
289                            "could not found expected ':'", self.get_mark())
290                del self.possible_simple_keys[level]
291
292    def save_possible_simple_key(self):
293        # The next token may start a simple key. We check if it's possible
294        # and save its position. This function is called for
295        #   ALIAS, ANCHOR, TAG, SCALAR(flow), '[', and '{'.
296
297        # Check if a simple key is required at the current position.
298        required = not self.flow_level and self.indent == self.column
299
300        # A simple key is required only if it is the first token in the current
301        # line. Therefore it is always allowed.
302        assert self.allow_simple_key or not required
303
304        # The next token might be a simple key. Let's save it's number and
305        # position.
306        if self.allow_simple_key:
307            self.remove_possible_simple_key()
308            token_number = self.tokens_taken+len(self.tokens)
309            key = SimpleKey(token_number, required,
310                    self.index, self.line, self.column, self.get_mark())
311            self.possible_simple_keys[self.flow_level] = key
312
313    def remove_possible_simple_key(self):
314        # Remove the saved possible key position at the current flow level.
315        if self.flow_level in self.possible_simple_keys:
316            key = self.possible_simple_keys[self.flow_level]
317           
318            if key.required:
319                raise ScannerError("while scanning a simple key", key.mark,
320                        "could not found expected ':'", self.get_mark())
321
322            del self.possible_simple_keys[self.flow_level]
323
324    # Indentation functions.
325
326    def unwind_indent(self, column):
327
328        ## In flow context, tokens should respect indentation.
329        ## Actually the condition should be `self.indent >= column` according to
330        ## the spec. But this condition will prohibit intuitively correct
331        ## constructions such as
332        ## key : {
333        ## }
334        #if self.flow_level and self.indent > column:
335        #    raise ScannerError(None, None,
336        #            "invalid intendation or unclosed '[' or '{'",
337        #            self.get_mark())
338
339        # In the flow context, indentation is ignored. We make the scanner less
340        # restrictive then specification requires.
341        if self.flow_level:
342            return
343
344        # In block context, we may need to issue the BLOCK-END tokens.
345        while self.indent > column:
346            mark = self.get_mark()
347            self.indent = self.indents.pop()
348            self.tokens.append(BlockEndToken(mark, mark))
349
350    def add_indent(self, column):
351        # Check if we need to increase indentation.
352        if self.indent < column:
353            self.indents.append(self.indent)
354            self.indent = column
355            return True
356        return False
357
358    # Fetchers.
359
360    def fetch_stream_start(self):
361        # We always add STREAM-START as the first token and STREAM-END as the
362        # last token.
363
364        # Read the token.
365        mark = self.get_mark()
366       
367        # Add STREAM-START.
368        self.tokens.append(StreamStartToken(mark, mark,
369            encoding=self.encoding))
370       
371
372    def fetch_stream_end(self):
373
374        # Set the current intendation to -1.
375        self.unwind_indent(-1)
376
377        # Reset simple keys.
378        self.remove_possible_simple_key()
379        self.allow_simple_key = False
380        self.possible_simple_keys = {}
381
382        # Read the token.
383        mark = self.get_mark()
384       
385        # Add STREAM-END.
386        self.tokens.append(StreamEndToken(mark, mark))
387
388        # The steam is finished.
389        self.done = True
390
391    def fetch_directive(self):
392       
393        # Set the current intendation to -1.
394        self.unwind_indent(-1)
395
396        # Reset simple keys.
397        self.remove_possible_simple_key()
398        self.allow_simple_key = False
399
400        # Scan and add DIRECTIVE.
401        self.tokens.append(self.scan_directive())
402
403    def fetch_document_start(self):
404        self.fetch_document_indicator(DocumentStartToken)
405
406    def fetch_document_end(self):
407        self.fetch_document_indicator(DocumentEndToken)
408
409    def fetch_document_indicator(self, TokenClass):
410
411        # Set the current intendation to -1.
412        self.unwind_indent(-1)
413
414        # Reset simple keys. Note that there could not be a block collection
415        # after '---'.
416        self.remove_possible_simple_key()
417        self.allow_simple_key = False
418
419        # Add DOCUMENT-START or DOCUMENT-END.
420        start_mark = self.get_mark()
421        self.forward(3)
422        end_mark = self.get_mark()
423        self.tokens.append(TokenClass(start_mark, end_mark))
424
425    def fetch_flow_sequence_start(self):
426        self.fetch_flow_collection_start(FlowSequenceStartToken)
427
428    def fetch_flow_mapping_start(self):
429        self.fetch_flow_collection_start(FlowMappingStartToken)
430
431    def fetch_flow_collection_start(self, TokenClass):
432
433        # '[' and '{' may start a simple key.
434        self.save_possible_simple_key()
435
436        # Increase the flow level.
437        self.flow_level += 1
438
439        # Simple keys are allowed after '[' and '{'.
440        self.allow_simple_key = True
441
442        # Add FLOW-SEQUENCE-START or FLOW-MAPPING-START.
443        start_mark = self.get_mark()
444        self.forward()
445        end_mark = self.get_mark()
446        self.tokens.append(TokenClass(start_mark, end_mark))
447
448    def fetch_flow_sequence_end(self):
449        self.fetch_flow_collection_end(FlowSequenceEndToken)
450
451    def fetch_flow_mapping_end(self):
452        self.fetch_flow_collection_end(FlowMappingEndToken)
453
454    def fetch_flow_collection_end(self, TokenClass):
455
456        # Reset possible simple key on the current level.
457        self.remove_possible_simple_key()
458
459        # Decrease the flow level.
460        self.flow_level -= 1
461
462        # No simple keys after ']' or '}'.
463        self.allow_simple_key = False
464
465        # Add FLOW-SEQUENCE-END or FLOW-MAPPING-END.
466        start_mark = self.get_mark()
467        self.forward()
468        end_mark = self.get_mark()
469        self.tokens.append(TokenClass(start_mark, end_mark))
470
471    def fetch_flow_entry(self):
472
473        # Simple keys are allowed after ','.
474        self.allow_simple_key = True
475
476        # Reset possible simple key on the current level.
477        self.remove_possible_simple_key()
478
479        # Add FLOW-ENTRY.
480        start_mark = self.get_mark()
481        self.forward()
482        end_mark = self.get_mark()
483        self.tokens.append(FlowEntryToken(start_mark, end_mark))
484
485    def fetch_block_entry(self):
486
487        # Block context needs additional checks.
488        if not self.flow_level:
489
490            # Are we allowed to start a new entry?
491            if not self.allow_simple_key:
492                raise ScannerError(None, None,
493                        "sequence entries are not allowed here",
494                        self.get_mark())
495
496            # We may need to add BLOCK-SEQUENCE-START.
497            if self.add_indent(self.column):
498                mark = self.get_mark()
499                self.tokens.append(BlockSequenceStartToken(mark, mark))
500
501        # It's an error for the block entry to occur in the flow context,
502        # but we let the parser detect this.
503        else:
504            pass
505
506        # Simple keys are allowed after '-'.
507        self.allow_simple_key = True
508
509        # Reset possible simple key on the current level.
510        self.remove_possible_simple_key()
511
512        # Add BLOCK-ENTRY.
513        start_mark = self.get_mark()
514        self.forward()
515        end_mark = self.get_mark()
516        self.tokens.append(BlockEntryToken(start_mark, end_mark))
517
518    def fetch_key(self):
519       
520        # Block context needs additional checks.
521        if not self.flow_level:
522
523            # Are we allowed to start a key (not nessesary a simple)?
524            if not self.allow_simple_key:
525                raise ScannerError(None, None,
526                        "mapping keys are not allowed here",
527                        self.get_mark())
528
529            # We may need to add BLOCK-MAPPING-START.
530            if self.add_indent(self.column):
531                mark = self.get_mark()
532                self.tokens.append(BlockMappingStartToken(mark, mark))
533
534        # Simple keys are allowed after '?' in the block context.
535        self.allow_simple_key = not self.flow_level
536
537        # Reset possible simple key on the current level.
538        self.remove_possible_simple_key()
539
540        # Add KEY.
541        start_mark = self.get_mark()
542        self.forward()
543        end_mark = self.get_mark()
544        self.tokens.append(KeyToken(start_mark, end_mark))
545
546    def fetch_value(self):
547
548        # Do we determine a simple key?
549        if self.flow_level in self.possible_simple_keys:
550
551            # Add KEY.
552            key = self.possible_simple_keys[self.flow_level]
553            del self.possible_simple_keys[self.flow_level]
554            self.tokens.insert(key.token_number-self.tokens_taken,
555                    KeyToken(key.mark, key.mark))
556
557            # If this key starts a new block mapping, we need to add
558            # BLOCK-MAPPING-START.
559            if not self.flow_level:
560                if self.add_indent(key.column):
561                    self.tokens.insert(key.token_number-self.tokens_taken,
562                            BlockMappingStartToken(key.mark, key.mark))
563
564            # There cannot be two simple keys one after another.
565            self.allow_simple_key = False
566
567        # It must be a part of a complex key.
568        else:
569           
570            # Block context needs additional checks.
571            # (Do we really need them? They will be catched by the parser
572            # anyway.)
573            if not self.flow_level:
574
575                # We are allowed to start a complex value if and only if
576                # we can start a simple key.
577                if not self.allow_simple_key:
578                    raise ScannerError(None, None,
579                            "mapping values are not allowed here",
580                            self.get_mark())
581
582            # If this value starts a new block mapping, we need to add
583            # BLOCK-MAPPING-START.  It will be detected as an error later by
584            # the parser.
585            if not self.flow_level:
586                if self.add_indent(self.column):
587                    mark = self.get_mark()
588                    self.tokens.append(BlockMappingStartToken(mark, mark))
589
590            # Simple keys are allowed after ':' in the block context.
591            self.allow_simple_key = not self.flow_level
592
593            # Reset possible simple key on the current level.
594            self.remove_possible_simple_key()
595
596        # Add VALUE.
597        start_mark = self.get_mark()
598        self.forward()
599        end_mark = self.get_mark()
600        self.tokens.append(ValueToken(start_mark, end_mark))
601
602    def fetch_alias(self):
603
604        # ALIAS could be a simple key.
605        self.save_possible_simple_key()
606
607        # No simple keys after ALIAS.
608        self.allow_simple_key = False
609
610        # Scan and add ALIAS.
611        self.tokens.append(self.scan_anchor(AliasToken))
612
613    def fetch_anchor(self):
614
615        # ANCHOR could start a simple key.
616        self.save_possible_simple_key()
617
618        # No simple keys after ANCHOR.
619        self.allow_simple_key = False
620
621        # Scan and add ANCHOR.
622        self.tokens.append(self.scan_anchor(AnchorToken))
623
624    def fetch_tag(self):
625
626        # TAG could start a simple key.
627        self.save_possible_simple_key()
628
629        # No simple keys after TAG.
630        self.allow_simple_key = False
631
632        # Scan and add TAG.
633        self.tokens.append(self.scan_tag())
634
635    def fetch_literal(self):
636        self.fetch_block_scalar(style='|')
637
638    def fetch_folded(self):
639        self.fetch_block_scalar(style='>')
640
641    def fetch_block_scalar(self, style):
642
643        # A simple key may follow a block scalar.
644        self.allow_simple_key = True
645
646        # Reset possible simple key on the current level.
647        self.remove_possible_simple_key()
648
649        # Scan and add SCALAR.
650        self.tokens.append(self.scan_block_scalar(style))
651
652    def fetch_single(self):
653        self.fetch_flow_scalar(style='\'')
654
655    def fetch_double(self):
656        self.fetch_flow_scalar(style='"')
657
658    def fetch_flow_scalar(self, style):
659
660        # A flow scalar could be a simple key.
661        self.save_possible_simple_key()
662
663        # No simple keys after flow scalars.
664        self.allow_simple_key = False
665
666        # Scan and add SCALAR.
667        self.tokens.append(self.scan_flow_scalar(style))
668
669    def fetch_plain(self):
670
671        # A plain scalar could be a simple key.
672        self.save_possible_simple_key()
673
674        # No simple keys after plain scalars. But note that `scan_plain` will
675        # change this flag if the scan is finished at the beginning of the
676        # line.
677        self.allow_simple_key = False
678
679        # Scan and add SCALAR. May change `allow_simple_key`.
680        self.tokens.append(self.scan_plain())
681
682    # Checkers.
683
684    def check_directive(self):
685
686        # DIRECTIVE:        ^ '%' ...
687        # The '%' indicator is already checked.
688        if self.column == 0:
689            return True
690
691    def check_document_start(self):
692
693        # DOCUMENT-START:   ^ '---' (' '|'\n')
694        if self.column == 0:
695            if self.prefix(3) == u'---'  \
696                    and self.peek(3) in u'\0 \t\r\n\x85\u2028\u2029':
697                return True
698
699    def check_document_end(self):
700
701        # DOCUMENT-END:     ^ '...' (' '|'\n')
702        if self.column == 0:
703            if self.prefix(3) == u'...'  \
704                    and self.peek(3) in u'\0 \t\r\n\x85\u2028\u2029':
705                return True
706
707    def check_block_entry(self):
708
709        # BLOCK-ENTRY:      '-' (' '|'\n')
710        return self.peek(1) in u'\0 \t\r\n\x85\u2028\u2029'
711
712    def check_key(self):
713
714        # KEY(flow context):    '?'
715        if self.flow_level:
716            return True
717
718        # KEY(block context):   '?' (' '|'\n')
719        else:
720            return self.peek(1) in u'\0 \t\r\n\x85\u2028\u2029'
721
722    def check_value(self):
723
724        # VALUE(flow context):  ':'
725        if self.flow_level:
726            return True
727
728        # VALUE(block context): ':' (' '|'\n')
729        else:
730            return self.peek(1) in u'\0 \t\r\n\x85\u2028\u2029'
731
732    def check_plain(self):
733
734        # A plain scalar may start with any non-space character except:
735        #   '-', '?', ':', ',', '[', ']', '{', '}',
736        #   '#', '&', '*', '!', '|', '>', '\'', '\"',
737        #   '%', '@', '`'.
738        #
739        # It may also start with
740        #   '-', '?', ':'
741        # if it is followed by a non-space character.
742        #
743        # Note that we limit the last rule to the block context (except the
744        # '-' character) because we want the flow context to be space
745        # independent.
746        ch = self.peek()
747        return ch not in u'\0 \t\r\n\x85\u2028\u2029-?:,[]{}#&*!|>\'\"%@`'  \
748                or (self.peek(1) not in u'\0 \t\r\n\x85\u2028\u2029'
749                        and (ch == u'-' or (not self.flow_level and ch in u'?:')))
750
751    # Scanners.
752
753    def scan_to_next_token(self):
754        # We ignore spaces, line breaks and comments.
755        # If we find a line break in the block context, we set the flag
756        # `allow_simple_key` on.
757        # The byte order mark is stripped if it's the first character in the
758        # stream. We do not yet support BOM inside the stream as the
759        # specification requires. Any such mark will be considered as a part
760        # of the document.
761        #
762        # TODO: We need to make tab handling rules more sane. A good rule is
763        #   Tabs cannot precede tokens
764        #   BLOCK-SEQUENCE-START, BLOCK-MAPPING-START, BLOCK-END,
765        #   KEY(block), VALUE(block), BLOCK-ENTRY
766        # So the checking code is
767        #   if <TAB>:
768        #       self.allow_simple_keys = False
769        # We also need to add the check for `allow_simple_keys == True` to
770        # `unwind_indent` before issuing BLOCK-END.
771        # Scanners for block, flow, and plain scalars need to be modified.
772
773        if self.index == 0 and self.peek() == u'\uFEFF':
774            self.forward()
775        found = False
776        while not found:
777            while self.peek() == u' ':
778                self.forward()
779            if self.peek() == u'#':
780                while self.peek() not in u'\0\r\n\x85\u2028\u2029':
781                    self.forward()
782            if self.scan_line_break():
783                if not self.flow_level:
784                    self.allow_simple_key = True
785            else:
786                found = True
787
788    def scan_directive(self):
789        # See the specification for details.
790        start_mark = self.get_mark()
791        self.forward()
792        name = self.scan_directive_name(start_mark)
793        value = None
794        if name == u'YAML':
795            value = self.scan_yaml_directive_value(start_mark)
796            end_mark = self.get_mark()
797        elif name == u'TAG':
798            value = self.scan_tag_directive_value(start_mark)
799            end_mark = self.get_mark()
800        else:
801            end_mark = self.get_mark()
802            while self.peek() not in u'\0\r\n\x85\u2028\u2029':
803                self.forward()
804        self.scan_directive_ignored_line(start_mark)
805        return DirectiveToken(name, value, start_mark, end_mark)
806
807    def scan_directive_name(self, start_mark):
808        # See the specification for details.
809        length = 0
810        ch = self.peek(length)
811        while u'0' <= ch <= u'9' or u'A' <= ch <= u'Z' or u'a' <= ch <= u'z'    \
812                or ch in u'-_':
813            length += 1
814            ch = self.peek(length)
815        if not length:
816            raise ScannerError("while scanning a directive", start_mark,
817                    "expected alphabetic or numeric character, but found %r"
818                    % ch.encode('utf-8'), self.get_mark())
819        value = self.prefix(length)
820        self.forward(length)
821        ch = self.peek()
822        if ch not in u'\0 \r\n\x85\u2028\u2029':
823            raise ScannerError("while scanning a directive", start_mark,
824                    "expected alphabetic or numeric character, but found %r"
825                    % ch.encode('utf-8'), self.get_mark())
826        return value
827
828    def scan_yaml_directive_value(self, start_mark):
829        # See the specification for details.
830        while self.peek() == u' ':
831            self.forward()
832        major = self.scan_yaml_directive_number(start_mark)
833        if self.peek() != '.':
834            raise ScannerError("while scanning a directive", start_mark,
835                    "expected a digit or '.', but found %r"
836                    % self.peek().encode('utf-8'),
837                    self.get_mark())
838        self.forward()
839        minor = self.scan_yaml_directive_number(start_mark)
840        if self.peek() not in u'\0 \r\n\x85\u2028\u2029':
841            raise ScannerError("while scanning a directive", start_mark,
842                    "expected a digit or ' ', but found %r"
843                    % self.peek().encode('utf-8'),
844                    self.get_mark())
845        return (major, minor)
846
847    def scan_yaml_directive_number(self, start_mark):
848        # See the specification for details.
849        ch = self.peek()
850        if not (u'0' <= ch <= u'9'):
851            raise ScannerError("while scanning a directive", start_mark,
852                    "expected a digit, but found %r" % ch.encode('utf-8'),
853                    self.get_mark())
854        length = 0
855        while u'0' <= self.peek(length) <= u'9':
856            length += 1
857        value = int(self.prefix(length))
858        self.forward(length)
859        return value
860
861    def scan_tag_directive_value(self, start_mark):
862        # See the specification for details.
863        while self.peek() == u' ':
864            self.forward()
865        handle = self.scan_tag_directive_handle(start_mark)
866        while self.peek() == u' ':
867            self.forward()
868        prefix = self.scan_tag_directive_prefix(start_mark)
869        return (handle, prefix)
870
871    def scan_tag_directive_handle(self, start_mark):
872        # See the specification for details.
873        value = self.scan_tag_handle('directive', start_mark)
874        ch = self.peek()
875        if ch != u' ':
876            raise ScannerError("while scanning a directive", start_mark,
877                    "expected ' ', but found %r" % ch.encode('utf-8'),
878                    self.get_mark())
879        return value
880
881    def scan_tag_directive_prefix(self, start_mark):
882        # See the specification for details.
883        value = self.scan_tag_uri('directive', start_mark)
884        ch = self.peek()
885        if ch not in u'\0 \r\n\x85\u2028\u2029':
886            raise ScannerError("while scanning a directive", start_mark,
887                    "expected ' ', but found %r" % ch.encode('utf-8'),
888                    self.get_mark())
889        return value
890
891    def scan_directive_ignored_line(self, start_mark):
892        # See the specification for details.
893        while self.peek() == u' ':
894            self.forward()
895        if self.peek() == u'#':
896            while self.peek() not in u'\0\r\n\x85\u2028\u2029':
897                self.forward()
898        ch = self.peek()
899        if ch not in u'\0\r\n\x85\u2028\u2029':
900            raise ScannerError("while scanning a directive", start_mark,
901                    "expected a comment or a line break, but found %r"
902                        % ch.encode('utf-8'), self.get_mark())
903        self.scan_line_break()
904
905    def scan_anchor(self, TokenClass):
906        # The specification does not restrict characters for anchors and
907        # aliases. This may lead to problems, for instance, the document:
908        #   [ *alias, value ]
909        # can be interpteted in two ways, as
910        #   [ "value" ]
911        # and
912        #   [ *alias , "value" ]
913        # Therefore we restrict aliases to numbers and ASCII letters.
914        start_mark = self.get_mark()
915        indicator = self.peek()
916        if indicator == u'*':
917            name = 'alias'
918        else:
919            name = 'anchor'
920        self.forward()
921        length = 0
922        ch = self.peek(length)
923        while u'0' <= ch <= u'9' or u'A' <= ch <= u'Z' or u'a' <= ch <= u'z'    \
924                or ch in u'-_':
925            length += 1
926            ch = self.peek(length)
927        if not length:
928            raise ScannerError("while scanning an %s" % name, start_mark,
929                    "expected alphabetic or numeric character, but found %r"
930                    % ch.encode('utf-8'), self.get_mark())
931        value = self.prefix(length)
932        self.forward(length)
933        ch = self.peek()
934        if ch not in u'\0 \t\r\n\x85\u2028\u2029?:,]}%@`':
935            raise ScannerError("while scanning an %s" % name, start_mark,
936                    "expected alphabetic or numeric character, but found %r"
937                    % ch.encode('utf-8'), self.get_mark())
938        end_mark = self.get_mark()
939        return TokenClass(value, start_mark, end_mark)
940
941    def scan_tag(self):
942        # See the specification for details.
943        start_mark = self.get_mark()
944        ch = self.peek(1)
945        if ch == u'<':
946            handle = None
947            self.forward(2)
948            suffix = self.scan_tag_uri('tag', start_mark)
949            if self.peek() != u'>':
950                raise ScannerError("while parsing a tag", start_mark,
951                        "expected '>', but found %r" % self.peek().encode('utf-8'),
952                        self.get_mark())
953            self.forward()
954        elif ch in u'\0 \t\r\n\x85\u2028\u2029':
955            handle = None
956            suffix = u'!'
957            self.forward()
958        else:
959            length = 1
960            use_handle = False
961            while ch not in u'\0 \r\n\x85\u2028\u2029':
962                if ch == u'!':
963                    use_handle = True
964                    break
965                length += 1
966                ch = self.peek(length)
967            handle = u'!'
968            if use_handle:
969                handle = self.scan_tag_handle('tag', start_mark)
970            else:
971                handle = u'!'
972                self.forward()
973            suffix = self.scan_tag_uri('tag', start_mark)
974        ch = self.peek()
975        if ch not in u'\0 \r\n\x85\u2028\u2029':
976            raise ScannerError("while scanning a tag", start_mark,
977                    "expected ' ', but found %r" % ch.encode('utf-8'),
978                    self.get_mark())
979        value = (handle, suffix)
980        end_mark = self.get_mark()
981        return TagToken(value, start_mark, end_mark)
982
983    def scan_block_scalar(self, style):
984        # See the specification for details.
985
986        if style == '>':
987            folded = True
988        else:
989            folded = False
990
991        chunks = []
992        start_mark = self.get_mark()
993
994        # Scan the header.
995        self.forward()
996        chomping, increment = self.scan_block_scalar_indicators(start_mark)
997        self.scan_block_scalar_ignored_line(start_mark)
998
999        # Determine the indentation level and go to the first non-empty line.
1000        min_indent = self.indent+1
1001        if min_indent < 1:
1002            min_indent = 1
1003        if increment is None:
1004            breaks, max_indent, end_mark = self.scan_block_scalar_indentation()
1005            indent = max(min_indent, max_indent)
1006        else:
1007            indent = min_indent+increment-1
1008            breaks, end_mark = self.scan_block_scalar_breaks(indent)
1009        line_break = u''
1010
1011        # Scan the inner part of the block scalar.
1012        while self.column == indent and self.peek() != u'\0':
1013            chunks.extend(breaks)
1014            leading_non_space = self.peek() not in u' \t'
1015            length = 0
1016            while self.peek(length) not in u'\0\r\n\x85\u2028\u2029':
1017                length += 1
1018            chunks.append(self.prefix(length))
1019            self.forward(length)
1020            line_break = self.scan_line_break()
1021            breaks, end_mark = self.scan_block_scalar_breaks(indent)
1022            if self.column == indent and self.peek() != u'\0':
1023
1024                # Unfortunately, folding rules are ambiguous.
1025                #
1026                # This is the folding according to the specification:
1027               
1028                if folded and line_break == u'\n'   \
1029                        and leading_non_space and self.peek() not in u' \t':
1030                    if not breaks:
1031                        chunks.append(u' ')
1032                else:
1033                    chunks.append(line_break)
1034               
1035                # This is Clark Evans's interpretation (also in the spec
1036                # examples):
1037                #
1038                #if folded and line_break == u'\n':
1039                #    if not breaks:
1040                #        if self.peek() not in ' \t':
1041                #            chunks.append(u' ')
1042                #        else:
1043                #            chunks.append(line_break)
1044                #else:
1045                #    chunks.append(line_break)
1046            else:
1047                break
1048
1049        # Chomp the tail.
1050        if chomping is not False:
1051            chunks.append(line_break)
1052        if chomping is True:
1053            chunks.extend(breaks)
1054
1055        # We are done.
1056        return ScalarToken(u''.join(chunks), False, start_mark, end_mark,
1057                style)
1058
1059    def scan_block_scalar_indicators(self, start_mark):
1060        # See the specification for details.
1061        chomping = None
1062        increment = None
1063        ch = self.peek()
1064        if ch in u'+-':
1065            if ch == '+':
1066                chomping = True
1067            else:
1068                chomping = False
1069            self.forward()
1070            ch = self.peek()
1071            if ch in u'0123456789':
1072                increment = int(ch)
1073                if increment == 0:
1074                    raise ScannerError("while scanning a block scalar", start_mark,
1075                            "expected indentation indicator in the range 1-9, but found 0",
1076                            self.get_mark())
1077                self.forward()
1078        elif ch in u'0123456789':
1079            increment = int(ch)
1080            if increment == 0:
1081                raise ScannerError("while scanning a block scalar", start_mark,
1082                        "expected indentation indicator in the range 1-9, but found 0",
1083                        self.get_mark())
1084            self.forward()
1085            ch = self.peek()
1086            if ch in u'+-':
1087                if ch == '+':
1088                    chomping = True
1089                else:
1090                    chomping = False
1091                self.forward()
1092        ch = self.peek()
1093        if ch not in u'\0 \r\n\x85\u2028\u2029':
1094            raise ScannerError("while scanning a block scalar", start_mark,
1095                    "expected chomping or indentation indicators, but found %r"
1096                        % ch.encode('utf-8'), self.get_mark())
1097        return chomping, increment
1098
1099    def scan_block_scalar_ignored_line(self, start_mark):
1100        # See the specification for details.
1101        while self.peek() == u' ':
1102            self.forward()
1103        if self.peek() == u'#':
1104            while self.peek() not in u'\0\r\n\x85\u2028\u2029':
1105                self.forward()
1106        ch = self.peek()
1107        if ch not in u'\0\r\n\x85\u2028\u2029':
1108            raise ScannerError("while scanning a block scalar", start_mark,
1109                    "expected a comment or a line break, but found %r"
1110                        % ch.encode('utf-8'), self.get_mark())
1111        self.scan_line_break()
1112
1113    def scan_block_scalar_indentation(self):
1114        # See the specification for details.
1115        chunks = []
1116        max_indent = 0
1117        end_mark = self.get_mark()
1118        while self.peek() in u' \r\n\x85\u2028\u2029':
1119            if self.peek() != u' ':
1120                chunks.append(self.scan_line_break())
1121                end_mark = self.get_mark()
1122            else:
1123                self.forward()
1124                if self.column > max_indent:
1125                    max_indent = self.column
1126        return chunks, max_indent, end_mark
1127
1128    def scan_block_scalar_breaks(self, indent):
1129        # See the specification for details.
1130        chunks = []
1131        end_mark = self.get_mark()
1132        while self.column < indent and self.peek() == u' ':
1133            self.forward()
1134        while self.peek() in u'\r\n\x85\u2028\u2029':
1135            chunks.append(self.scan_line_break())
1136            end_mark = self.get_mark()
1137            while self.column < indent and self.peek() == u' ':
1138                self.forward()
1139        return chunks, end_mark
1140
1141    def scan_flow_scalar(self, style):
1142        # See the specification for details.
1143        # Note that we loose indentation rules for quoted scalars. Quoted
1144        # scalars don't need to adhere indentation because " and ' clearly
1145        # mark the beginning and the end of them. Therefore we are less
1146        # restrictive then the specification requires. We only need to check
1147        # that document separators are not included in scalars.
1148        if style == '"':
1149            double = True
1150        else:
1151            double = False
1152        chunks = []
1153        start_mark = self.get_mark()
1154        quote = self.peek()
1155        self.forward()
1156        chunks.extend(self.scan_flow_scalar_non_spaces(double, start_mark))
1157        while self.peek() != quote:
1158            chunks.extend(self.scan_flow_scalar_spaces(double, start_mark))
1159            chunks.extend(self.scan_flow_scalar_non_spaces(double, start_mark))
1160        self.forward()
1161        end_mark = self.get_mark()
1162        return ScalarToken(u''.join(chunks), False, start_mark, end_mark,
1163                style)
1164
1165    ESCAPE_REPLACEMENTS = {
1166        u'0':   u'\0',
1167        u'a':   u'\x07',
1168        u'b':   u'\x08',
1169        u't':   u'\x09',
1170        u'\t':  u'\x09',
1171        u'n':   u'\x0A',
1172        u'v':   u'\x0B',
1173        u'f':   u'\x0C',
1174        u'r':   u'\x0D',
1175        u'e':   u'\x1B',
1176        u' ':   u'\x20',
1177        u'\"':  u'\"',
1178        u'\\':  u'\\',
1179        u'N':   u'\x85',
1180        u'_':   u'\xA0',
1181        u'L':   u'\u2028',
1182        u'P':   u'\u2029',
1183    }
1184
1185    ESCAPE_CODES = {
1186        u'x':   2,
1187        u'u':   4,
1188        u'U':   8,
1189    }
1190
1191    def scan_flow_scalar_non_spaces(self, double, start_mark):
1192        # See the specification for details.
1193        chunks = []
1194        while True:
1195            length = 0
1196            while self.peek(length) not in u'\'\"\\\0 \t\r\n\x85\u2028\u2029':
1197                length += 1
1198            if length:
1199                chunks.append(self.prefix(length))
1200                self.forward(length)
1201            ch = self.peek()
1202            if not double and ch == u'\'' and self.peek(1) == u'\'':
1203                chunks.append(u'\'')
1204                self.forward(2)
1205            elif (double and ch == u'\'') or (not double and ch in u'\"\\'):
1206                chunks.append(ch)
1207                self.forward()
1208            elif double and ch == u'\\':
1209                self.forward()
1210                ch = self.peek()
1211                if ch in self.ESCAPE_REPLACEMENTS:
1212                    chunks.append(self.ESCAPE_REPLACEMENTS[ch])
1213                    self.forward()
1214                elif ch in self.ESCAPE_CODES:
1215                    length = self.ESCAPE_CODES[ch]
1216                    self.forward()
1217                    for k in range(length):
1218                        if self.peek(k) not in u'0123456789ABCDEFabcdef':
1219                            raise ScannerError("while scanning a double-quoted scalar", start_mark,
1220                                    "expected escape sequence of %d hexdecimal numbers, but found %r" %
1221                                        (length, self.peek(k).encode('utf-8')), self.get_mark())
1222                    code = int(self.prefix(length), 16)
1223                    chunks.append(unichr(code))
1224                    self.forward(length)
1225                elif ch in u'\r\n\x85\u2028\u2029':
1226                    self.scan_line_break()
1227                    chunks.extend(self.scan_flow_scalar_breaks(double, start_mark))
1228                else:
1229                    raise ScannerError("while scanning a double-quoted scalar", start_mark,
1230                            "found unknown escape character %r" % ch.encode('utf-8'), self.get_mark())
1231            else:
1232                return chunks
1233
1234    def scan_flow_scalar_spaces(self, double, start_mark):
1235        # See the specification for details.
1236        chunks = []
1237        length = 0
1238        while self.peek(length) in u' \t':
1239            length += 1
1240        whitespaces = self.prefix(length)
1241        self.forward(length)
1242        ch = self.peek()
1243        if ch == u'\0':
1244            raise ScannerError("while scanning a quoted scalar", start_mark,
1245                    "found unexpected end of stream", self.get_mark())
1246        elif ch in u'\r\n\x85\u2028\u2029':
1247            line_break = self.scan_line_break()
1248            breaks = self.scan_flow_scalar_breaks(double, start_mark)
1249            if line_break != u'\n':
1250                chunks.append(line_break)
1251            elif not breaks:
1252                chunks.append(u' ')
1253            chunks.extend(breaks)
1254        else:
1255            chunks.append(whitespaces)
1256        return chunks
1257
1258    def scan_flow_scalar_breaks(self, double, start_mark):
1259        # See the specification for details.
1260        chunks = []
1261        while True:
1262            # Instead of checking indentation, we check for document
1263            # separators.
1264            prefix = self.prefix(3)
1265            if (prefix == u'---' or prefix == u'...')   \
1266                    and self.peek(3) in u'\0 \t\r\n\x85\u2028\u2029':
1267                raise ScannerError("while scanning a quoted scalar", start_mark,
1268                        "found unexpected document separator", self.get_mark())
1269            while self.peek() in u' \t':
1270                self.forward()
1271            if self.peek() in u'\r\n\x85\u2028\u2029':
1272                chunks.append(self.scan_line_break())
1273            else:
1274                return chunks
1275
1276    def scan_plain(self):
1277        # See the specification for details.
1278        # We add an additional restriction for the flow context:
1279        #   plain scalars in the flow context cannot contain ',', ':' and '?'.
1280        # We also keep track of the `allow_simple_key` flag here.
1281        # Indentation rules are loosed for the flow context.
1282        chunks = []
1283        start_mark = self.get_mark()
1284        end_mark = start_mark
1285        indent = self.indent+1
1286        # We allow zero indentation for scalars, but then we need to check for
1287        # document separators at the beginning of the line.
1288        #if indent == 0:
1289        #    indent = 1
1290        spaces = []
1291        while True:
1292            length = 0
1293            if self.peek() == u'#':
1294                break
1295            while True:
1296                ch = self.peek(length)
1297                if ch in u'\0 \t\r\n\x85\u2028\u2029'   \
1298                        or (not self.flow_level and ch == u':' and
1299                                self.peek(length+1) in u'\0 \t\r\n\x85\u2028\u2029') \
1300                        or (self.flow_level and ch in u',:?[]{}'):
1301                    break
1302                length += 1
1303            # It's not clear what we should do with ':' in the flow context.
1304            if (self.flow_level and ch == u':'
1305                    and self.peek(length+1) not in u'\0 \t\r\n\x85\u2028\u2029,[]{}'):
1306                self.forward(length)
1307                raise ScannerError("while scanning a plain scalar", start_mark,
1308                    "found unexpected ':'", self.get_mark(),
1309                    "Please check http://pyyaml.org/wiki/YAMLColonInFlowContext for details.")
1310            if length == 0:
1311                break
1312            self.allow_simple_key = False
1313            chunks.extend(spaces)
1314            chunks.append(self.prefix(length))
1315            self.forward(length)
1316            end_mark = self.get_mark()
1317            spaces = self.scan_plain_spaces(indent, start_mark)
1318            if not spaces or self.peek() == u'#' \
1319                    or (not self.flow_level and self.column < indent):
1320                break
1321        return ScalarToken(u''.join(chunks), True, start_mark, end_mark)
1322
1323    def scan_plain_spaces(self, indent, start_mark):
1324        # See the specification for details.
1325        # The specification is really confusing about tabs in plain scalars.
1326        # We just forbid them completely. Do not use tabs in YAML!
1327        chunks = []
1328        length = 0
1329        while self.peek(length) in u' ':
1330            length += 1
1331        whitespaces = self.prefix(length)
1332        self.forward(length)
1333        ch = self.peek()
1334        if ch in u'\r\n\x85\u2028\u2029':
1335            line_break = self.scan_line_break()
1336            self.allow_simple_key = True
1337            prefix = self.prefix(3)
1338            if (prefix == u'---' or prefix == u'...')   \
1339                    and self.peek(3) in u'\0 \t\r\n\x85\u2028\u2029':
1340                return
1341            breaks = []
1342            while self.peek() in u' \r\n\x85\u2028\u2029':
1343                if self.peek() == ' ':
1344                    self.forward()
1345                else:
1346                    breaks.append(self.scan_line_break())
1347                    prefix = self.prefix(3)
1348                    if (prefix == u'---' or prefix == u'...')   \
1349                            and self.peek(3) in u'\0 \t\r\n\x85\u2028\u2029':
1350                        return
1351            if line_break != u'\n':
1352                chunks.append(line_break)
1353            elif not breaks:
1354                chunks.append(u' ')
1355            chunks.extend(breaks)
1356        elif whitespaces:
1357            chunks.append(whitespaces)
1358        return chunks
1359
1360    def scan_tag_handle(self, name, start_mark):
1361        # See the specification for details.
1362        # For some strange reasons, the specification does not allow '_' in
1363        # tag handles. I have allowed it anyway.
1364        ch = self.peek()
1365        if ch != u'!':
1366            raise ScannerError("while scanning a %s" % name, start_mark,
1367                    "expected '!', but found %r" % ch.encode('utf-8'),
1368                    self.get_mark())
1369        length = 1
1370        ch = self.peek(length)
1371        if ch != u' ':
1372            while u'0' <= ch <= u'9' or u'A' <= ch <= u'Z' or u'a' <= ch <= u'z'    \
1373                    or ch in u'-_':
1374                length += 1
1375                ch = self.peek(length)
1376            if ch != u'!':
1377                self.forward(length)
1378                raise ScannerError("while scanning a %s" % name, start_mark,
1379                        "expected '!', but found %r" % ch.encode('utf-8'),
1380                        self.get_mark())
1381            length += 1
1382        value = self.prefix(length)
1383        self.forward(length)
1384        return value
1385
1386    def scan_tag_uri(self, name, start_mark):
1387        # See the specification for details.
1388        # Note: we do not check if URI is well-formed.
1389        chunks = []
1390        length = 0
1391        ch = self.peek(length)
1392        while u'0' <= ch <= u'9' or u'A' <= ch <= u'Z' or u'a' <= ch <= u'z'    \
1393                or ch in u'-;/?:@&=+$,_.!~*\'()[]%':
1394            if ch == u'%':
1395                chunks.append(self.prefix(length))
1396                self.forward(length)
1397                length = 0
1398                chunks.append(self.scan_uri_escapes(name, start_mark))
1399            else:
1400                length += 1
1401            ch = self.peek(length)
1402        if length:
1403            chunks.append(self.prefix(length))
1404            self.forward(length)
1405            length = 0
1406        if not chunks:
1407            raise ScannerError("while parsing a %s" % name, start_mark,
1408                    "expected URI, but found %r" % ch.encode('utf-8'),
1409                    self.get_mark())
1410        return u''.join(chunks)
1411
1412    def scan_uri_escapes(self, name, start_mark):
1413        # See the specification for details.
1414        bytes = []
1415        mark = self.get_mark()
1416        while self.peek() == u'%':
1417            self.forward()
1418            for k in range(2):
1419                if self.peek(k) not in u'0123456789ABCDEFabcdef':
1420                    raise ScannerError("while scanning a %s" % name, start_mark,
1421                            "expected URI escape sequence of 2 hexdecimal numbers, but found %r" %
1422                                (self.peek(k).encode('utf-8')), self.get_mark())
1423            bytes.append(chr(int(self.prefix(2), 16)))
1424            self.forward(2)
1425        try:
1426            value = unicode(''.join(bytes), 'utf-8')
1427        except UnicodeDecodeError, exc:
1428            raise ScannerError("while scanning a %s" % name, start_mark, str(exc), mark)
1429        return value
1430
1431    def scan_line_break(self):
1432        # Transforms:
1433        #   '\r\n'      :   '\n'
1434        #   '\r'        :   '\n'
1435        #   '\n'        :   '\n'
1436        #   '\x85'      :   '\n'
1437        #   '\u2028'    :   '\u2028'
1438        #   '\u2029     :   '\u2029'
1439        #   default     :   ''
1440        ch = self.peek()
1441        if ch in u'\r\n\x85':
1442            if self.prefix(2) == u'\r\n':
1443                self.forward(2)
1444            else:
1445                self.forward()
1446            return u'\n'
1447        elif ch in u'\u2028\u2029':
1448            self.forward()
1449            return ch
1450        return u''
1451
1452#try:
1453#    import psyco
1454#    psyco.bind(Scanner)
1455#except ImportError:
1456#    pass
1457
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