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- ######################## BEGIN LICENSE BLOCK ########################
- # The Original Code is Mozilla Universal charset detector code.
- #
- # The Initial Developer of the Original Code is
- # Shy Shalom
- # Portions created by the Initial Developer are Copyright (C) 2005
- # the Initial Developer. All Rights Reserved.
- #
- # Contributor(s):
- # Mark Pilgrim - port to Python
- #
- # This library is free software; you can redistribute it and/or
- # modify it under the terms of the GNU Lesser General Public
- # License as published by the Free Software Foundation; either
- # version 2.1 of the License, or (at your option) any later version.
- #
- # This library is distributed in the hope that it will be useful,
- # but WITHOUT ANY WARRANTY; without even the implied warranty of
- # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- # Lesser General Public License for more details.
- #
- # You should have received a copy of the GNU Lesser General Public
- # License along with this library; if not, write to the Free Software
- # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
- # 02110-1301 USA
- ######################### END LICENSE BLOCK #########################
- from .charsetprober import CharSetProber
- from .constants import eNotMe, eDetecting
- from .compat import wrap_ord
- # This prober doesn't actually recognize a language or a charset.
- # It is a helper prober for the use of the Hebrew model probers
- ### General ideas of the Hebrew charset recognition ###
- #
- # Four main charsets exist in Hebrew:
- # "ISO-8859-8" - Visual Hebrew
- # "windows-1255" - Logical Hebrew
- # "ISO-8859-8-I" - Logical Hebrew
- # "x-mac-hebrew" - ?? Logical Hebrew ??
- #
- # Both "ISO" charsets use a completely identical set of code points, whereas
- # "windows-1255" and "x-mac-hebrew" are two different proper supersets of
- # these code points. windows-1255 defines additional characters in the range
- # 0x80-0x9F as some misc punctuation marks as well as some Hebrew-specific
- # diacritics and additional 'Yiddish' ligature letters in the range 0xc0-0xd6.
- # x-mac-hebrew defines similar additional code points but with a different
- # mapping.
- #
- # As far as an average Hebrew text with no diacritics is concerned, all four
- # charsets are identical with respect to code points. Meaning that for the
- # main Hebrew alphabet, all four map the same values to all 27 Hebrew letters
- # (including final letters).
- #
- # The dominant difference between these charsets is their directionality.
- # "Visual" directionality means that the text is ordered as if the renderer is
- # not aware of a BIDI rendering algorithm. The renderer sees the text and
- # draws it from left to right. The text itself when ordered naturally is read
- # backwards. A buffer of Visual Hebrew generally looks like so:
- # "[last word of first line spelled backwards] [whole line ordered backwards
- # and spelled backwards] [first word of first line spelled backwards]
- # [end of line] [last word of second line] ... etc' "
- # adding punctuation marks, numbers and English text to visual text is
- # naturally also "visual" and from left to right.
- #
- # "Logical" directionality means the text is ordered "naturally" according to
- # the order it is read. It is the responsibility of the renderer to display
- # the text from right to left. A BIDI algorithm is used to place general
- # punctuation marks, numbers and English text in the text.
- #
- # Texts in x-mac-hebrew are almost impossible to find on the Internet. From
- # what little evidence I could find, it seems that its general directionality
- # is Logical.
- #
- # To sum up all of the above, the Hebrew probing mechanism knows about two
- # charsets:
- # Visual Hebrew - "ISO-8859-8" - backwards text - Words and sentences are
- # backwards while line order is natural. For charset recognition purposes
- # the line order is unimportant (In fact, for this implementation, even
- # word order is unimportant).
- # Logical Hebrew - "windows-1255" - normal, naturally ordered text.
- #
- # "ISO-8859-8-I" is a subset of windows-1255 and doesn't need to be
- # specifically identified.
- # "x-mac-hebrew" is also identified as windows-1255. A text in x-mac-hebrew
- # that contain special punctuation marks or diacritics is displayed with
- # some unconverted characters showing as question marks. This problem might
- # be corrected using another model prober for x-mac-hebrew. Due to the fact
- # that x-mac-hebrew texts are so rare, writing another model prober isn't
- # worth the effort and performance hit.
- #
- #### The Prober ####
- #
- # The prober is divided between two SBCharSetProbers and a HebrewProber,
- # all of which are managed, created, fed data, inquired and deleted by the
- # SBCSGroupProber. The two SBCharSetProbers identify that the text is in
- # fact some kind of Hebrew, Logical or Visual. The final decision about which
- # one is it is made by the HebrewProber by combining final-letter scores
- # with the scores of the two SBCharSetProbers to produce a final answer.
- #
- # The SBCSGroupProber is responsible for stripping the original text of HTML
- # tags, English characters, numbers, low-ASCII punctuation characters, spaces
- # and new lines. It reduces any sequence of such characters to a single space.
- # The buffer fed to each prober in the SBCS group prober is pure text in
- # high-ASCII.
- # The two SBCharSetProbers (model probers) share the same language model:
- # Win1255Model.
- # The first SBCharSetProber uses the model normally as any other
- # SBCharSetProber does, to recognize windows-1255, upon which this model was
- # built. The second SBCharSetProber is told to make the pair-of-letter
- # lookup in the language model backwards. This in practice exactly simulates
- # a visual Hebrew model using the windows-1255 logical Hebrew model.
- #
- # The HebrewProber is not using any language model. All it does is look for
- # final-letter evidence suggesting the text is either logical Hebrew or visual
- # Hebrew. Disjointed from the model probers, the results of the HebrewProber
- # alone are meaningless. HebrewProber always returns 0.00 as confidence
- # since it never identifies a charset by itself. Instead, the pointer to the
- # HebrewProber is passed to the model probers as a helper "Name Prober".
- # When the Group prober receives a positive identification from any prober,
- # it asks for the name of the charset identified. If the prober queried is a
- # Hebrew model prober, the model prober forwards the call to the
- # HebrewProber to make the final decision. In the HebrewProber, the
- # decision is made according to the final-letters scores maintained and Both
- # model probers scores. The answer is returned in the form of the name of the
- # charset identified, either "windows-1255" or "ISO-8859-8".
- # windows-1255 / ISO-8859-8 code points of interest
- FINAL_KAF = 0xea
- NORMAL_KAF = 0xeb
- FINAL_MEM = 0xed
- NORMAL_MEM = 0xee
- FINAL_NUN = 0xef
- NORMAL_NUN = 0xf0
- FINAL_PE = 0xf3
- NORMAL_PE = 0xf4
- FINAL_TSADI = 0xf5
- NORMAL_TSADI = 0xf6
- # Minimum Visual vs Logical final letter score difference.
- # If the difference is below this, don't rely solely on the final letter score
- # distance.
- MIN_FINAL_CHAR_DISTANCE = 5
- # Minimum Visual vs Logical model score difference.
- # If the difference is below this, don't rely at all on the model score
- # distance.
- MIN_MODEL_DISTANCE = 0.01
- VISUAL_HEBREW_NAME = "ISO-8859-8"
- LOGICAL_HEBREW_NAME = "windows-1255"
- class HebrewProber(CharSetProber):
- def __init__(self):
- CharSetProber.__init__(self)
- self._mLogicalProber = None
- self._mVisualProber = None
- self.reset()
- def reset(self):
- self._mFinalCharLogicalScore = 0
- self._mFinalCharVisualScore = 0
- # The two last characters seen in the previous buffer,
- # mPrev and mBeforePrev are initialized to space in order to simulate
- # a word delimiter at the beginning of the data
- self._mPrev = ' '
- self._mBeforePrev = ' '
- # These probers are owned by the group prober.
- def set_model_probers(self, logicalProber, visualProber):
- self._mLogicalProber = logicalProber
- self._mVisualProber = visualProber
- def is_final(self, c):
- return wrap_ord(c) in [FINAL_KAF, FINAL_MEM, FINAL_NUN, FINAL_PE,
- FINAL_TSADI]
- def is_non_final(self, c):
- # The normal Tsadi is not a good Non-Final letter due to words like
- # 'lechotet' (to chat) containing an apostrophe after the tsadi. This
- # apostrophe is converted to a space in FilterWithoutEnglishLetters
- # causing the Non-Final tsadi to appear at an end of a word even
- # though this is not the case in the original text.
- # The letters Pe and Kaf rarely display a related behavior of not being
- # a good Non-Final letter. Words like 'Pop', 'Winamp' and 'Mubarak'
- # for example legally end with a Non-Final Pe or Kaf. However, the
- # benefit of these letters as Non-Final letters outweighs the damage
- # since these words are quite rare.
- return wrap_ord(c) in [NORMAL_KAF, NORMAL_MEM, NORMAL_NUN, NORMAL_PE]
- def feed(self, aBuf):
- # Final letter analysis for logical-visual decision.
- # Look for evidence that the received buffer is either logical Hebrew
- # or visual Hebrew.
- # The following cases are checked:
- # 1) A word longer than 1 letter, ending with a final letter. This is
- # an indication that the text is laid out "naturally" since the
- # final letter really appears at the end. +1 for logical score.
- # 2) A word longer than 1 letter, ending with a Non-Final letter. In
- # normal Hebrew, words ending with Kaf, Mem, Nun, Pe or Tsadi,
- # should not end with the Non-Final form of that letter. Exceptions
- # to this rule are mentioned above in isNonFinal(). This is an
- # indication that the text is laid out backwards. +1 for visual
- # score
- # 3) A word longer than 1 letter, starting with a final letter. Final
- # letters should not appear at the beginning of a word. This is an
- # indication that the text is laid out backwards. +1 for visual
- # score.
- #
- # The visual score and logical score are accumulated throughout the
- # text and are finally checked against each other in GetCharSetName().
- # No checking for final letters in the middle of words is done since
- # that case is not an indication for either Logical or Visual text.
- #
- # We automatically filter out all 7-bit characters (replace them with
- # spaces) so the word boundary detection works properly. [MAP]
- if self.get_state() == eNotMe:
- # Both model probers say it's not them. No reason to continue.
- return eNotMe
- aBuf = self.filter_high_bit_only(aBuf)
- for cur in aBuf:
- if cur == ' ':
- # We stand on a space - a word just ended
- if self._mBeforePrev != ' ':
- # next-to-last char was not a space so self._mPrev is not a
- # 1 letter word
- if self.is_final(self._mPrev):
- # case (1) [-2:not space][-1:final letter][cur:space]
- self._mFinalCharLogicalScore += 1
- elif self.is_non_final(self._mPrev):
- # case (2) [-2:not space][-1:Non-Final letter][
- # cur:space]
- self._mFinalCharVisualScore += 1
- else:
- # Not standing on a space
- if ((self._mBeforePrev == ' ') and
- (self.is_final(self._mPrev)) and (cur != ' ')):
- # case (3) [-2:space][-1:final letter][cur:not space]
- self._mFinalCharVisualScore += 1
- self._mBeforePrev = self._mPrev
- self._mPrev = cur
- # Forever detecting, till the end or until both model probers return
- # eNotMe (handled above)
- return eDetecting
- def get_charset_name(self):
- # Make the decision: is it Logical or Visual?
- # If the final letter score distance is dominant enough, rely on it.
- finalsub = self._mFinalCharLogicalScore - self._mFinalCharVisualScore
- if finalsub >= MIN_FINAL_CHAR_DISTANCE:
- return LOGICAL_HEBREW_NAME
- if finalsub <= -MIN_FINAL_CHAR_DISTANCE:
- return VISUAL_HEBREW_NAME
- # It's not dominant enough, try to rely on the model scores instead.
- modelsub = (self._mLogicalProber.get_confidence()
- - self._mVisualProber.get_confidence())
- if modelsub > MIN_MODEL_DISTANCE:
- return LOGICAL_HEBREW_NAME
- if modelsub < -MIN_MODEL_DISTANCE:
- return VISUAL_HEBREW_NAME
- # Still no good, back to final letter distance, maybe it'll save the
- # day.
- if finalsub < 0.0:
- return VISUAL_HEBREW_NAME
- # (finalsub > 0 - Logical) or (don't know what to do) default to
- # Logical.
- return LOGICAL_HEBREW_NAME
- def get_state(self):
- # Remain active as long as any of the model probers are active.
- if (self._mLogicalProber.get_state() == eNotMe) and \
- (self._mVisualProber.get_state() == eNotMe):
- return eNotMe
- return eDetecting
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