######################## 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 CharacterCategory, ProbingState, SequenceLikelihood
class SingleByteCharSetProber(CharSetProber):
SAMPLE_SIZE = 64
SB_ENOUGH_REL_THRESHOLD = 1024 # 0.25 * SAMPLE_SIZE^2
POSITIVE_SHORTCUT_THRESHOLD = 0.95
NEGATIVE_SHORTCUT_THRESHOLD = 0.05
def __init__(self, model, reversed=False, name_prober=None):
super(SingleByteCharSetProber, self).__init__()
self._model = model
# TRUE if we need to reverse every pair in the model lookup
self._reversed = reversed
# Optional auxiliary prober for name decision
self._name_prober = name_prober
self._last_order = None
self._seq_counters = None
self._total_seqs = None
self._total_char = None
self._freq_char = None
self.reset()
def reset(self):
super(SingleByteCharSetProber, self).reset()
# char order of last character
self._last_order = 255
self._seq_counters = [0] * SequenceLikelihood.get_num_categories()
self._total_seqs = 0
self._total_char = 0
# characters that fall in our sampling range
self._freq_char = 0
@property
def charset_name(self):
if self._name_prober:
return self._name_prober.charset_name
else:
return self._model['charset_name']
@property
def language(self):
if self._name_prober:
return self._name_prober.language
else:
return self._model.get('language')
def feed(self, byte_str):
if not self._model['keep_english_letter']:
byte_str = self.filter_international_words(byte_str)
if not byte_str:
return self.state
char_to_order_map = self._model['char_to_order_map']
for i, c in enumerate(byte_str):
# XXX: Order is in range 1-64, so one would think we want 0-63 here,
# but that leads to 27 more test failures than before.
order = char_to_order_map[c]
# XXX: This was SYMBOL_CAT_ORDER before, with a value of 250, but
# CharacterCategory.SYMBOL is actually 253, so we use CONTROL
# to make it closer to the original intent. The only difference
# is whether or not we count digits and control characters for
# _total_char purposes.
if order < CharacterCategory.CONTROL:
self._total_char += 1
if order < self.SAMPLE_SIZE:
self._freq_char += 1
if self._last_order < self.SAMPLE_SIZE:
self._total_seqs += 1
if not self._reversed:
i = (self._last_order * self.SAMPLE_SIZE) + order
model = self._model['precedence_matrix'][i]
else: # reverse the order of the letters in the lookup
i = (order * self.SAMPLE_SIZE) + self._last_order
model = self._model['precedence_matrix'][i]
self._seq_counters[model] += 1
self._last_order = order
charset_name = self._model['charset_name']
if self.state == ProbingState.DETECTING:
if self._total_seqs > self.SB_ENOUGH_REL_THRESHOLD:
confidence = self.get_confidence()
if confidence > self.POSITIVE_SHORTCUT_THRESHOLD:
self.logger.debug('%s confidence = %s, we have a winner',
charset_name, confidence)
self._state = ProbingState.FOUND_IT
elif confidence < self.NEGATIVE_SHORTCUT_THRESHOLD:
self.logger.debug('%s confidence = %s, below negative '
'shortcut threshhold %s', charset_name,
confidence,
self.NEGATIVE_SHORTCUT_THRESHOLD)
self._state = ProbingState.NOT_ME
return self.state
def get_confidence(self):
r = 0.01
if self._total_seqs > 0:
r = ((1.0 * self._seq_counters[SequenceLikelihood.POSITIVE]) /
self._total_seqs / self._model['typical_positive_ratio'])
r = r * self._freq_char / self._total_char
if r >= 1.0:
r = 0.99
return r
