latin1prober.py

######################## BEGIN LICENSE BLOCK ########################
# The Original Code is Mozilla Universal charset detector code.
#
# The Initial Developer of the Original Code is
# Netscape Communications Corporation.
# Portions created by the Initial Developer are Copyright (C) 2001
# the Initial Developer. All Rights Reserved.
#
# Contributor(s):
#   Mark Pilgrim - port to Python
#   Shy Shalom - original C code
#
# 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 .enums import ProbingState

FREQ_CAT_NUM = 4

UDF = 0  # undefined
OTH = 1  # other
ASC = 2  # ascii capital letter
ASS = 3  # ascii small letter
ACV = 4  # accent capital vowel
ACO = 5  # accent capital other
ASV = 6  # accent small vowel
ASO = 7  # accent small other
CLASS_NUM = 8  # total classes

Latin1_CharToClass = (
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 00 - 07
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 08 - 0F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 10 - 17
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 18 - 1F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 20 - 27
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 28 - 2F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 30 - 37
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 38 - 3F
    OTH, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   # 40 - 47
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   # 48 - 4F
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   # 50 - 57
    ASC, ASC, ASC, OTH, OTH, OTH, OTH, OTH,   # 58 - 5F
    OTH, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   # 60 - 67
    ASS, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   # 68 - 6F
    ASS, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   # 70 - 77
    ASS, ASS, ASS, OTH, OTH, OTH, OTH, OTH,   # 78 - 7F
    OTH, UDF, OTH, ASO, OTH, OTH, OTH, OTH,   # 80 - 87
    OTH, OTH, ACO, OTH, ACO, UDF, ACO, UDF,   # 88 - 8F
    UDF, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 90 - 97
    OTH, OTH, ASO, OTH, ASO, UDF, ASO, ACO,   # 98 - 9F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # A0 - A7
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # A8 - AF
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # B0 - B7
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # B8 - BF
    ACV, ACV, ACV, ACV, ACV, ACV, ACO, ACO,   # C0 - C7
    ACV, ACV, ACV, ACV, ACV, ACV, ACV, ACV,   # C8 - CF
    ACO, ACO, ACV, ACV, ACV, ACV, ACV, OTH,   # D0 - D7
    ACV, ACV, ACV, ACV, ACV, ACO, ACO, ACO,   # D8 - DF
    ASV, ASV, ASV, ASV, ASV, ASV, ASO, ASO,   # E0 - E7
    ASV, ASV, ASV, ASV, ASV, ASV, ASV, ASV,   # E8 - EF
    ASO, ASO, ASV, ASV, ASV, ASV, ASV, OTH,   # F0 - F7
    ASV, ASV, ASV, ASV, ASV, ASO, ASO, ASO,   # F8 - FF
)

# 0 : illegal
# 1 : very unlikely
# 2 : normal
# 3 : very likely
Latin1ClassModel = (
# UDF OTH ASC ASS ACV ACO ASV ASO
    0,  0,  0,  0,  0,  0,  0,  0,  # UDF
    0,  3,  3,  3,  3,  3,  3,  3,  # OTH
    0,  3,  3,  3,  3,  3,  3,  3,  # ASC
    0,  3,  3,  3,  1,  1,  3,  3,  # ASS
    0,  3,  3,  3,  1,  2,  1,  2,  # ACV
    0,  3,  3,  3,  3,  3,  3,  3,  # ACO
    0,  3,  1,  3,  1,  1,  1,  3,  # ASV
    0,  3,  1,  3,  1,  1,  3,  3,  # ASO
)


class Latin1Prober(CharSetProber):
    def __init__(self):
        super(Latin1Prober, self).__init__()
        self._last_char_class = None
        self._freq_counter = None
        self.reset()

    def reset(self):
        self._last_char_class = OTH
        self._freq_counter = [0] * FREQ_CAT_NUM
        CharSetProber.reset(self)

    @property
    def charset_name(self):
        return "ISO-8859-1"

    @property
    def language(self):
        return ""

    def feed(self, byte_str):
        byte_str = self.filter_with_english_letters(byte_str)
        for c in byte_str:
            char_class = Latin1_CharToClass[c]
            freq = Latin1ClassModel[(self._last_char_class * CLASS_NUM)
                                    + char_class]
            if freq == 0:
                self._state = ProbingState.NOT_ME
                break
            self._freq_counter[freq] += 1
            self._last_char_class = char_class

        return self.state

    def get_confidence(self):
        if self.state == ProbingState.NOT_ME:
            return 0.01

        total = sum(self._freq_counter)
        if total < 0.01:
            confidence = 0.0
        else:
            confidence = ((self._freq_counter[3] - self._freq_counter[1] * 20.0)
                          / total)
        if confidence < 0.0:
            confidence = 0.0
        # lower the confidence of latin1 so that other more accurate
        # detector can take priority.
        confidence = confidence * 0.73
        return confidence