Source code for chardet.chardistribution

######################## BEGIN LICENSE BLOCK ########################
# The Original Code is Mozilla Communicator client code.
#
# The Initial Developer of the Original Code is
# Netscape Communications Corporation.
# Portions created by the Initial Developer are Copyright (C) 1998
# 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 .big5freq import (
    BIG5_CHAR_TO_FREQ_ORDER,
    BIG5_TABLE_SIZE,
    BIG5_TYPICAL_DISTRIBUTION_RATIO,
)
from .euckrfreq import (
    EUCKR_CHAR_TO_FREQ_ORDER,
    EUCKR_TABLE_SIZE,
    EUCKR_TYPICAL_DISTRIBUTION_RATIO,
)
from .euctwfreq import (
    EUCTW_CHAR_TO_FREQ_ORDER,
    EUCTW_TABLE_SIZE,
    EUCTW_TYPICAL_DISTRIBUTION_RATIO,
)
from .gb2312freq import (
    GB2312_CHAR_TO_FREQ_ORDER,
    GB2312_TABLE_SIZE,
    GB2312_TYPICAL_DISTRIBUTION_RATIO,
)
from .jisfreq import (
    JIS_CHAR_TO_FREQ_ORDER,
    JIS_TABLE_SIZE,
    JIS_TYPICAL_DISTRIBUTION_RATIO,
)
from .johabfreq import JOHAB_TO_EUCKR_ORDER_TABLE


[docs]class CharDistributionAnalysis: ENOUGH_DATA_THRESHOLD = 1024 SURE_YES = 0.99 SURE_NO = 0.01 MINIMUM_DATA_THRESHOLD = 3 def __init__(self): # Mapping table to get frequency order from char order (get from # GetOrder()) self._char_to_freq_order = None self._table_size = None # Size of above table # This is a constant value which varies from language to language, # used in calculating confidence. See # http://www.mozilla.org/projects/intl/UniversalCharsetDetection.html # for further detail. self.typical_distribution_ratio = None self._done = None self._total_chars = None self._freq_chars = None self.reset()
[docs] def reset(self): """reset analyser, clear any state""" # If this flag is set to True, detection is done and conclusion has # been made self._done = False self._total_chars = 0 # Total characters encountered # The number of characters whose frequency order is less than 512 self._freq_chars = 0
[docs] def feed(self, char, char_len): """feed a character with known length""" if char_len == 2: # we only care about 2-bytes character in our distribution analysis order = self.get_order(char) else: order = -1 if order >= 0: self._total_chars += 1 # order is valid if order < self._table_size: if 512 > self._char_to_freq_order[order]: self._freq_chars += 1
[docs] def get_confidence(self): """return confidence based on existing data""" # if we didn't receive any character in our consideration range, # return negative answer if self._total_chars <= 0 or self._freq_chars <= self.MINIMUM_DATA_THRESHOLD: return self.SURE_NO if self._total_chars != self._freq_chars: r = self._freq_chars / ( (self._total_chars - self._freq_chars) * self.typical_distribution_ratio ) if r < self.SURE_YES: return r # normalize confidence (we don't want to be 100% sure) return self.SURE_YES
[docs] def got_enough_data(self): # It is not necessary to receive all data to draw conclusion. # For charset detection, certain amount of data is enough return self._total_chars > self.ENOUGH_DATA_THRESHOLD
[docs] def get_order(self, byte_str): # We do not handle characters based on the original encoding string, # but convert this encoding string to a number, here called order. # This allows multiple encodings of a language to share one frequency # table. return -1
[docs]class EUCTWDistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = EUCTW_CHAR_TO_FREQ_ORDER self._table_size = EUCTW_TABLE_SIZE self.typical_distribution_ratio = EUCTW_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): # for euc-TW encoding, we are interested # first byte range: 0xc4 -- 0xfe # second byte range: 0xa1 -- 0xfe # no validation needed here. State machine has done that first_char = byte_str[0] if first_char >= 0xC4: return 94 * (first_char - 0xC4) + byte_str[1] - 0xA1 else: return -1
[docs]class EUCKRDistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = EUCKR_CHAR_TO_FREQ_ORDER self._table_size = EUCKR_TABLE_SIZE self.typical_distribution_ratio = EUCKR_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): # for euc-KR encoding, we are interested # first byte range: 0xb0 -- 0xfe # second byte range: 0xa1 -- 0xfe # no validation needed here. State machine has done that first_char = byte_str[0] if first_char >= 0xB0: return 94 * (first_char - 0xB0) + byte_str[1] - 0xA1 else: return -1
[docs]class JOHABDistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = EUCKR_CHAR_TO_FREQ_ORDER self._table_size = EUCKR_TABLE_SIZE self.typical_distribution_ratio = EUCKR_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): first_char = byte_str[0] if 0x88 <= first_char < 0xD4: code = first_char * 256 + byte_str[1] return JOHAB_TO_EUCKR_ORDER_TABLE.get(code, -1) return -1
[docs]class GB2312DistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = GB2312_CHAR_TO_FREQ_ORDER self._table_size = GB2312_TABLE_SIZE self.typical_distribution_ratio = GB2312_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): # for GB2312 encoding, we are interested # first byte range: 0xb0 -- 0xfe # second byte range: 0xa1 -- 0xfe # no validation needed here. State machine has done that first_char, second_char = byte_str[0], byte_str[1] if (first_char >= 0xB0) and (second_char >= 0xA1): return 94 * (first_char - 0xB0) + second_char - 0xA1 else: return -1
[docs]class Big5DistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = BIG5_CHAR_TO_FREQ_ORDER self._table_size = BIG5_TABLE_SIZE self.typical_distribution_ratio = BIG5_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): # for big5 encoding, we are interested # first byte range: 0xa4 -- 0xfe # second byte range: 0x40 -- 0x7e , 0xa1 -- 0xfe # no validation needed here. State machine has done that first_char, second_char = byte_str[0], byte_str[1] if first_char >= 0xA4: if second_char >= 0xA1: return 157 * (first_char - 0xA4) + second_char - 0xA1 + 63 else: return 157 * (first_char - 0xA4) + second_char - 0x40 else: return -1
[docs]class SJISDistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = JIS_CHAR_TO_FREQ_ORDER self._table_size = JIS_TABLE_SIZE self.typical_distribution_ratio = JIS_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): # for sjis encoding, we are interested # first byte range: 0x81 -- 0x9f , 0xe0 -- 0xfe # second byte range: 0x40 -- 0x7e, 0x81 -- oxfe # no validation needed here. State machine has done that first_char, second_char = byte_str[0], byte_str[1] if (first_char >= 0x81) and (first_char <= 0x9F): order = 188 * (first_char - 0x81) elif (first_char >= 0xE0) and (first_char <= 0xEF): order = 188 * (first_char - 0xE0 + 31) else: return -1 order = order + second_char - 0x40 if second_char > 0x7F: order = -1 return order
[docs]class EUCJPDistributionAnalysis(CharDistributionAnalysis): def __init__(self): super().__init__() self._char_to_freq_order = JIS_CHAR_TO_FREQ_ORDER self._table_size = JIS_TABLE_SIZE self.typical_distribution_ratio = JIS_TYPICAL_DISTRIBUTION_RATIO
[docs] def get_order(self, byte_str): # for euc-JP encoding, we are interested # first byte range: 0xa0 -- 0xfe # second byte range: 0xa1 -- 0xfe # no validation needed here. State machine has done that char = byte_str[0] if char >= 0xA0: return 94 * (char - 0xA1) + byte_str[1] - 0xA1 else: return -1