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authorShubham Saini <shubham6405@gmail.com>2019-08-05 08:32:33 +0000
committerShubham Saini <shubham6405@gmail.com>2019-08-05 08:32:33 +0000
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1######################## BEGIN LICENSE BLOCK ########################
2# The Original Code is Mozilla Universal charset detector code.
3#
4# The Initial Developer of the Original Code is
5# Shy Shalom
6# Portions created by the Initial Developer are Copyright (C) 2005
7# the Initial Developer. All Rights Reserved.
8#
9# Contributor(s):
10# Mark Pilgrim - port to Python
11#
12# This library is free software; you can redistribute it and/or
13# modify it under the terms of the GNU Lesser General Public
14# License as published by the Free Software Foundation; either
15# version 2.1 of the License, or (at your option) any later version.
16#
17# This library is distributed in the hope that it will be useful,
18# but WITHOUT ANY WARRANTY; without even the implied warranty of
19# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20# Lesser General Public License for more details.
21#
22# You should have received a copy of the GNU Lesser General Public
23# License along with this library; if not, write to the Free Software
24# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
25# 02110-1301 USA
26######################### END LICENSE BLOCK #########################
27
28from .charsetprober import CharSetProber
29from .enums import ProbingState
30
31# This prober doesn't actually recognize a language or a charset.
32# It is a helper prober for the use of the Hebrew model probers
33
34### General ideas of the Hebrew charset recognition ###
35#
36# Four main charsets exist in Hebrew:
37# "ISO-8859-8" - Visual Hebrew
38# "windows-1255" - Logical Hebrew
39# "ISO-8859-8-I" - Logical Hebrew
40# "x-mac-hebrew" - ?? Logical Hebrew ??
41#
42# Both "ISO" charsets use a completely identical set of code points, whereas
43# "windows-1255" and "x-mac-hebrew" are two different proper supersets of
44# these code points. windows-1255 defines additional characters in the range
45# 0x80-0x9F as some misc punctuation marks as well as some Hebrew-specific
46# diacritics and additional 'Yiddish' ligature letters in the range 0xc0-0xd6.
47# x-mac-hebrew defines similar additional code points but with a different
48# mapping.
49#
50# As far as an average Hebrew text with no diacritics is concerned, all four
51# charsets are identical with respect to code points. Meaning that for the
52# main Hebrew alphabet, all four map the same values to all 27 Hebrew letters
53# (including final letters).
54#
55# The dominant difference between these charsets is their directionality.
56# "Visual" directionality means that the text is ordered as if the renderer is
57# not aware of a BIDI rendering algorithm. The renderer sees the text and
58# draws it from left to right. The text itself when ordered naturally is read
59# backwards. A buffer of Visual Hebrew generally looks like so:
60# "[last word of first line spelled backwards] [whole line ordered backwards
61# and spelled backwards] [first word of first line spelled backwards]
62# [end of line] [last word of second line] ... etc' "
63# adding punctuation marks, numbers and English text to visual text is
64# naturally also "visual" and from left to right.
65#
66# "Logical" directionality means the text is ordered "naturally" according to
67# the order it is read. It is the responsibility of the renderer to display
68# the text from right to left. A BIDI algorithm is used to place general
69# punctuation marks, numbers and English text in the text.
70#
71# Texts in x-mac-hebrew are almost impossible to find on the Internet. From
72# what little evidence I could find, it seems that its general directionality
73# is Logical.
74#
75# To sum up all of the above, the Hebrew probing mechanism knows about two
76# charsets:
77# Visual Hebrew - "ISO-8859-8" - backwards text - Words and sentences are
78# backwards while line order is natural. For charset recognition purposes
79# the line order is unimportant (In fact, for this implementation, even
80# word order is unimportant).
81# Logical Hebrew - "windows-1255" - normal, naturally ordered text.
82#
83# "ISO-8859-8-I" is a subset of windows-1255 and doesn't need to be
84# specifically identified.
85# "x-mac-hebrew" is also identified as windows-1255. A text in x-mac-hebrew
86# that contain special punctuation marks or diacritics is displayed with
87# some unconverted characters showing as question marks. This problem might
88# be corrected using another model prober for x-mac-hebrew. Due to the fact
89# that x-mac-hebrew texts are so rare, writing another model prober isn't
90# worth the effort and performance hit.
91#
92#### The Prober ####
93#
94# The prober is divided between two SBCharSetProbers and a HebrewProber,
95# all of which are managed, created, fed data, inquired and deleted by the
96# SBCSGroupProber. The two SBCharSetProbers identify that the text is in
97# fact some kind of Hebrew, Logical or Visual. The final decision about which
98# one is it is made by the HebrewProber by combining final-letter scores
99# with the scores of the two SBCharSetProbers to produce a final answer.
100#
101# The SBCSGroupProber is responsible for stripping the original text of HTML
102# tags, English characters, numbers, low-ASCII punctuation characters, spaces
103# and new lines. It reduces any sequence of such characters to a single space.
104# The buffer fed to each prober in the SBCS group prober is pure text in
105# high-ASCII.
106# The two SBCharSetProbers (model probers) share the same language model:
107# Win1255Model.
108# The first SBCharSetProber uses the model normally as any other
109# SBCharSetProber does, to recognize windows-1255, upon which this model was
110# built. The second SBCharSetProber is told to make the pair-of-letter
111# lookup in the language model backwards. This in practice exactly simulates
112# a visual Hebrew model using the windows-1255 logical Hebrew model.
113#
114# The HebrewProber is not using any language model. All it does is look for
115# final-letter evidence suggesting the text is either logical Hebrew or visual
116# Hebrew. Disjointed from the model probers, the results of the HebrewProber
117# alone are meaningless. HebrewProber always returns 0.00 as confidence
118# since it never identifies a charset by itself. Instead, the pointer to the
119# HebrewProber is passed to the model probers as a helper "Name Prober".
120# When the Group prober receives a positive identification from any prober,
121# it asks for the name of the charset identified. If the prober queried is a
122# Hebrew model prober, the model prober forwards the call to the
123# HebrewProber to make the final decision. In the HebrewProber, the
124# decision is made according to the final-letters scores maintained and Both
125# model probers scores. The answer is returned in the form of the name of the
126# charset identified, either "windows-1255" or "ISO-8859-8".
127
128class HebrewProber(CharSetProber):
129 # windows-1255 / ISO-8859-8 code points of interest
130 FINAL_KAF = 0xea
131 NORMAL_KAF = 0xeb
132 FINAL_MEM = 0xed
133 NORMAL_MEM = 0xee
134 FINAL_NUN = 0xef
135 NORMAL_NUN = 0xf0
136 FINAL_PE = 0xf3
137 NORMAL_PE = 0xf4
138 FINAL_TSADI = 0xf5
139 NORMAL_TSADI = 0xf6
140
141 # Minimum Visual vs Logical final letter score difference.
142 # If the difference is below this, don't rely solely on the final letter score
143 # distance.
144 MIN_FINAL_CHAR_DISTANCE = 5
145
146 # Minimum Visual vs Logical model score difference.
147 # If the difference is below this, don't rely at all on the model score
148 # distance.
149 MIN_MODEL_DISTANCE = 0.01
150
151 VISUAL_HEBREW_NAME = "ISO-8859-8"
152 LOGICAL_HEBREW_NAME = "windows-1255"
153
154 def __init__(self):
155 super(HebrewProber, self).__init__()
156 self._final_char_logical_score = None
157 self._final_char_visual_score = None
158 self._prev = None
159 self._before_prev = None
160 self._logical_prober = None
161 self._visual_prober = None
162 self.reset()
163
164 def reset(self):
165 self._final_char_logical_score = 0
166 self._final_char_visual_score = 0
167 # The two last characters seen in the previous buffer,
168 # mPrev and mBeforePrev are initialized to space in order to simulate
169 # a word delimiter at the beginning of the data
170 self._prev = ' '
171 self._before_prev = ' '
172 # These probers are owned by the group prober.
173
174 def set_model_probers(self, logicalProber, visualProber):
175 self._logical_prober = logicalProber
176 self._visual_prober = visualProber
177
178 def is_final(self, c):
179 return c in [self.FINAL_KAF, self.FINAL_MEM, self.FINAL_NUN,
180 self.FINAL_PE, self.FINAL_TSADI]
181
182 def is_non_final(self, c):
183 # The normal Tsadi is not a good Non-Final letter due to words like
184 # 'lechotet' (to chat) containing an apostrophe after the tsadi. This
185 # apostrophe is converted to a space in FilterWithoutEnglishLetters
186 # causing the Non-Final tsadi to appear at an end of a word even
187 # though this is not the case in the original text.
188 # The letters Pe and Kaf rarely display a related behavior of not being
189 # a good Non-Final letter. Words like 'Pop', 'Winamp' and 'Mubarak'
190 # for example legally end with a Non-Final Pe or Kaf. However, the
191 # benefit of these letters as Non-Final letters outweighs the damage
192 # since these words are quite rare.
193 return c in [self.NORMAL_KAF, self.NORMAL_MEM,
194 self.NORMAL_NUN, self.NORMAL_PE]
195
196 def feed(self, byte_str):
197 # Final letter analysis for logical-visual decision.
198 # Look for evidence that the received buffer is either logical Hebrew
199 # or visual Hebrew.
200 # The following cases are checked:
201 # 1) A word longer than 1 letter, ending with a final letter. This is
202 # an indication that the text is laid out "naturally" since the
203 # final letter really appears at the end. +1 for logical score.
204 # 2) A word longer than 1 letter, ending with a Non-Final letter. In
205 # normal Hebrew, words ending with Kaf, Mem, Nun, Pe or Tsadi,
206 # should not end with the Non-Final form of that letter. Exceptions
207 # to this rule are mentioned above in isNonFinal(). This is an
208 # indication that the text is laid out backwards. +1 for visual
209 # score
210 # 3) A word longer than 1 letter, starting with a final letter. Final
211 # letters should not appear at the beginning of a word. This is an
212 # indication that the text is laid out backwards. +1 for visual
213 # score.
214 #
215 # The visual score and logical score are accumulated throughout the
216 # text and are finally checked against each other in GetCharSetName().
217 # No checking for final letters in the middle of words is done since
218 # that case is not an indication for either Logical or Visual text.
219 #
220 # We automatically filter out all 7-bit characters (replace them with
221 # spaces) so the word boundary detection works properly. [MAP]
222
223 if self.state == ProbingState.NOT_ME:
224 # Both model probers say it's not them. No reason to continue.
225 return ProbingState.NOT_ME
226
227 byte_str = self.filter_high_byte_only(byte_str)
228
229 for cur in byte_str:
230 if cur == ' ':
231 # We stand on a space - a word just ended
232 if self._before_prev != ' ':
233 # next-to-last char was not a space so self._prev is not a
234 # 1 letter word
235 if self.is_final(self._prev):
236 # case (1) [-2:not space][-1:final letter][cur:space]
237 self._final_char_logical_score += 1
238 elif self.is_non_final(self._prev):
239 # case (2) [-2:not space][-1:Non-Final letter][
240 # cur:space]
241 self._final_char_visual_score += 1
242 else:
243 # Not standing on a space
244 if ((self._before_prev == ' ') and
245 (self.is_final(self._prev)) and (cur != ' ')):
246 # case (3) [-2:space][-1:final letter][cur:not space]
247 self._final_char_visual_score += 1
248 self._before_prev = self._prev
249 self._prev = cur
250
251 # Forever detecting, till the end or until both model probers return
252 # ProbingState.NOT_ME (handled above)
253 return ProbingState.DETECTING
254
255 @property
256 def charset_name(self):
257 # Make the decision: is it Logical or Visual?
258 # If the final letter score distance is dominant enough, rely on it.
259 finalsub = self._final_char_logical_score - self._final_char_visual_score
260 if finalsub >= self.MIN_FINAL_CHAR_DISTANCE:
261 return self.LOGICAL_HEBREW_NAME
262 if finalsub <= -self.MIN_FINAL_CHAR_DISTANCE:
263 return self.VISUAL_HEBREW_NAME
264
265 # It's not dominant enough, try to rely on the model scores instead.
266 modelsub = (self._logical_prober.get_confidence()
267 - self._visual_prober.get_confidence())
268 if modelsub > self.MIN_MODEL_DISTANCE:
269 return self.LOGICAL_HEBREW_NAME
270 if modelsub < -self.MIN_MODEL_DISTANCE:
271 return self.VISUAL_HEBREW_NAME
272
273 # Still no good, back to final letter distance, maybe it'll save the
274 # day.
275 if finalsub < 0.0:
276 return self.VISUAL_HEBREW_NAME
277
278 # (finalsub > 0 - Logical) or (don't know what to do) default to
279 # Logical.
280 return self.LOGICAL_HEBREW_NAME
281
282 @property
283 def language(self):
284 return 'Hebrew'
285
286 @property
287 def state(self):
288 # Remain active as long as any of the model probers are active.
289 if (self._logical_prober.state == ProbingState.NOT_ME) and \
290 (self._visual_prober.state == ProbingState.NOT_ME):
291 return ProbingState.NOT_ME
292 return ProbingState.DETECTING