Add constants BOM_UTF8, BOM_UTF16, BOM_UTF16_LE, BOM_UTF16_BE,

doerwalter · doerwalter · commit 474458da4894 · 2002-06-04T15:16:29.000Z
BOM_UTF32, BOM_UTF32_LE and BOM_UTF32_BE that represent the Byte Order Mark in UTF-8, UTF-16 and UTF-32 encodings for little and big endian systems. The old names BOM32_* and BOM64_* were off by a factor of 2. This closes SF bug http://www.python.org/sf/555360
diff --git a/Doc/lib/libcodecs.tex b/Doc/lib/libcodecs.tex
@@ -142,16 +142,21 @@ \section{\module{codecs} ---
 \begin{datadesc}{BOM}
 \dataline{BOM_BE}
 \dataline{BOM_LE}
-\dataline{BOM32_BE}
-\dataline{BOM32_LE}
-\dataline{BOM64_BE}
-\dataline{BOM64_LE}
-These constants define the byte order marks (BOM) used in data
-streams to indicate the byte order used in the stream or file.
-\constant{BOM} is either \constant{BOM_BE} or \constant{BOM_LE}
-depending on the platform's native byte order, while the others
-represent big endian (\samp{_BE} suffix) and little endian
-(\samp{_LE} suffix) byte order using 32-bit and 64-bit encodings.
+\dataline{BOM_UTF8}
+\dataline{BOM_UTF16}
+\dataline{BOM_UTF16_BE}
+\dataline{BOM_UTF16_LE}
+\dataline{BOM_UTF32}
+\dataline{BOM_UTF32_BE}
+\dataline{BOM_UTF32_LE}
+These constants define various encodings of the Unicode byte order mark
+(BOM) used in UTF-16 and UTF-32 data streams to indicate the byte order
+used in the stream or file and in UTF-8 as a Unicode signature.
+\constant{BOM_UTF16} is either \constant{BOM_UTF16_BE} or
+\constant{BOM_UTF16_LE} depending on the platform's native byte order,
+\constant{BOM} is an alias for \constant{BOM_UTF16}, \constant{BOM_LE}
+for \constant{BOM_UTF16_LE} and \constant{BOM_BE} for \constant{BOM_UTF16_BE}.
+The others represent the BOM in UTF-8 and UTF-32 encodings.
 \end{datadesc}
 
 
diff --git a/Lib/codecs.py b/Lib/codecs.py
@@ -18,29 +18,44 @@
           'Failed to load the builtin codecs: %s' % why
 
 __all__ = ["register", "lookup", "open", "EncodedFile", "BOM", "BOM_BE",
-           "BOM_LE", "BOM32_BE", "BOM32_LE", "BOM64_BE", "BOM64_LE"]
+           "BOM_LE", "BOM32_BE", "BOM32_LE", "BOM64_BE", "BOM64_LE",
+           "BOM_UTF8", "BOM_UTF16", "BOM_UTF16_LE", "BOM_UTF16_BE",
+           "BOM_UTF32", "BOM_UTF32_LE", "BOM_UTF32_BE"]
 
 ### Constants
 
 #
-# Byte Order Mark (BOM) and its possible values (BOM_BE, BOM_LE)
+# Byte Order Mark (BOM = ZERO WIDTH NO-BREAK SPACE = U+FEFF)
+# and its possible byte string values
+# for UTF8/UTF16/UTF32 output and little/big endian machines
 #
-BOM = struct.pack('=H', 0xFEFF)
-#
-BOM_BE = BOM32_BE = '\376\377'
-#       corresponds to Unicode U+FEFF in UTF-16 on big endian
-#       platforms == ZERO WIDTH NO-BREAK SPACE
-BOM_LE = BOM32_LE = '\377\376'
-#       corresponds to Unicode U+FFFE in UTF-16 on little endian
-#       platforms == defined as being an illegal Unicode character
 
-#
-# 64-bit Byte Order Marks
-#
-BOM64_BE = '\000\000\376\377'
-#       corresponds to Unicode U+0000FEFF in UCS-4
-BOM64_LE = '\377\376\000\000'
-#       corresponds to Unicode U+0000FFFE in UCS-4
+# UTF-8
+BOM_UTF8 = '\xef\xbb\xbf'
+
+# UTF-16, little endian
+BOM_LE = BOM_UTF16_LE = '\xff\xfe'
+
+# UTF-16, big endian
+BOM_BE = BOM_UTF16_BE = '\xfe\xff'
+
+# UTF-32, little endian
+BOM_UTF32_LE = '\xff\xfe\x00\x00'
+
+# UTF-32, big endian
+BOM_UTF32_BE = '\x00\x00\xfe\xff'
+
+# UTF-16, native endianness
+BOM = BOM_UTF16 = struct.pack('=H', 0xFEFF)
+
+# UTF-32, native endianness
+BOM_UTF32 = struct.pack('=L', 0x0000FEFF)
+
+# Old broken names (don't use in new code)
+BOM32_LE = BOM_UTF16_LE
+BOM32_BE = BOM_UTF16_BE
+BOM64_LE = BOM_UTF32_LE
+BOM64_BE = BOM_UTF32_BE
 
 
 ### Codec base classes (defining the API)
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -124,6 +124,12 @@ Extension modules
 
 Library
 
+- Constants BOM_UTF8, BOM_UTF16, BOM_UTF16_LE, BOM_UTF16_BE,
+  BOM_UTF32, BOM_UTF32_LE and BOM_UTF32_BE that represent the Byte
+  Order Mark in UTF-8, UTF-16 and UTF-32 encodings for little and
+  big endian systems were added to the codecs module. The old names
+  BOM32_* and BOM64_* were off by a factor of 2.
+
 - added degree/radian conversion functions to the math module.
 
 - ftplib.retrlines() now tests for callback is None rather than testing
