Added a prober for MacRoman encoding.

MacRoman is not in particularly common use anymore, as it has been
deprecated by Mac OS for over a decade. However, there are programs such
as Microsoft Office for Mac that didn't get the memo, and will output in
MacRoman by default.

The MacRoman detector works similarly to the Latin-1 detector, but
starts at a lower probability.

chardet/macromanprober.py

@@ -0,0 +1,160 @@
+######################## BEGIN LICENSE BLOCK ########################
+# This code was modified from latin1prober.py by Rob Speer <rob@lumino.so>.
+# 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):
+#   Rob Speer - adapt to MacRoman encoding
+#   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
+ODD = 8  # character that is unlikely to appear
+CLASS_NUM = 9  # total classes
+
+# The change from Latin1 is that we explicitly look for extended characters
+# that are infrequently-occurring symbols, and consider them to always be
+# improbable. This should let MacRoman get out of the way of more likely
+# encodings in most situations.
+
+# fmt: off
+MacRoman_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
+    ACV, ACV, ACO, ACV, ACO, ACV, ACV, ASV,  # 80 - 87
+    ASV, ASV, ASV, ASV, ASV, ASO, ASV, ASV,  # 88 - 8F
+    ASV, ASV, ASV, ASV, ASV, ASV, ASO, ASV,  # 90 - 97
+    ASV, ASV, ASV, ASV, ASV, ASV, ASV, ASV,  # 98 - 9F
+    OTH, OTH, OTH, OTH, OTH, OTH, OTH, ASO,  # A0 - A7
+    OTH, OTH, ODD, ODD, OTH, OTH, ACV, ACV,  # A8 - AF
+    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,  # B0 - B7
+    OTH, OTH, OTH, OTH, OTH, OTH, ASV, ASV,  # B8 - BF
+    OTH, OTH, ODD, OTH, ODD, OTH, OTH, OTH,  # C0 - C7
+    OTH, OTH, OTH, ACV, ACV, ACV, ACV, ASV,  # C8 - CF
+    OTH, OTH, OTH, OTH, OTH, OTH, OTH, ODD,  # D0 - D7
+    ASV, ACV, ODD, OTH, OTH, OTH, OTH, OTH,  # D8 - DF
+    OTH, OTH, OTH, OTH, OTH, ACV, ACV, ACV,  # E0 - E7
+    ACV, ACV, ACV, ACV, ACV, ACV, ACV, ACV,  # E8 - EF
+    ODD, ACV, ACV, ACV, ACV, ASV, ODD, ODD,  # F0 - F7
+    ODD, ODD, ODD, ODD, ODD, ODD, ODD, ODD,  # F8 - FF
+)
+
+# 0 : illegal
+# 1 : very unlikely
+# 2 : normal
+# 3 : very likely
+MacRomanClassModel = (
+# UDF OTH ASC ASS ACV ACO ASV ASO ODD
+    0,  0,  0,  0,  0,  0,  0,  0,  0,  # UDF
+    0,  3,  3,  3,  3,  3,  3,  3,  1,  # OTH
+    0,  3,  3,  3,  3,  3,  3,  3,  1,  # ASC
+    0,  3,  3,  3,  1,  1,  3,  3,  1,  # ASS
+    0,  3,  3,  3,  1,  2,  1,  2,  1,  # ACV
+    0,  3,  3,  3,  3,  3,  3,  3,  1,  # ACO
+    0,  3,  1,  3,  1,  1,  1,  3,  1,  # ASV
+    0,  3,  1,  3,  1,  1,  3,  3,  1,  # ASO
+    0,  1,  1,  1,  1,  1,  1,  1,  1,  # ODD
+)
+# fmt: on
+
+
+class MacRomanProber(CharSetProber):
+    def __init__(self):
+        super().__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
+
+        # express the prior that MacRoman is a somewhat rare encoding;
+        # this can be done by starting out in a slightly improbable state
+        # that must be overcome
+        self._freq_counter[2] = 10
+
+        super().reset()
+
+    @property
+    def charset_name(self):
+        return "MacRoman"
+
+    @property
+    def language(self):
+        return ""
+
+    def feed(self, byte_str):
+        byte_str = self.remove_xml_tags(byte_str)
+        for c in byte_str:
+            char_class = MacRoman_CharToClass[c]
+            freq = MacRomanClassModel[(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)
+        confidence = (
+            0.0
+            if total < 0.01
+            else (self._freq_counter[3] - self._freq_counter[1] * 20.0) / total
+        )
+        confidence = max(confidence, 0.0)
+        # lower the confidence of MacRoman so that other more accurate
+        # detector can take priority.
+        confidence *= 0.73
+        return confidence

chardet/universaldetector.py

@@ -44,6 +44,7 @@ class a user of ``chardet`` should use.
 from .enums import InputState, LanguageFilter, ProbingState
 from .escprober import EscCharSetProber
 from .latin1prober import Latin1Prober
+from .macromanprober import MacRomanProber
 from .mbcsgroupprober import MBCSGroupProber
 from .sbcsgroupprober import SBCSGroupProber
 from .utf1632prober import UTF1632Prober
@@ -242,6 +243,7 @@ def feed(self, byte_str):
                 if self.lang_filter & LanguageFilter.NON_CJK:
                     self._charset_probers.append(SBCSGroupProber())
                 self._charset_probers.append(Latin1Prober())
+                self._charset_probers.append(MacRomanProber())
             for prober in self._charset_probers:
                 if prober.feed(byte_str) == ProbingState.FOUND_IT:
                     self.result = {