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Umlauts, encodings, sitecustomize.py

Jeff Epler jepler at unpythonic.net
Tue Nov 9 15:07:58 EST 2004 
On Tue, Nov 09, 2004 at 07:52:58PM +0100, F. GEIGER wrote:
> "Jeff Epler" <jepler at unpythonic.net> schrieb im Newsbeitrag
> news:mailman.6167.1100019195.5135.python-list at python.org...
> 
> > You should note that chr(0x84) is *not* a-umlaut in iso-8859-1.  That's
> chr(0xe4).  You may be using one of these Windows-specific encodings:
> >     cp437.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> >     cp775.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> >     cp850.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> >     cp852.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> >     cp857.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> >     cp861.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> >     cp865.py:       0x0084: 0x00e4, # LATIN SMALL LETTER A WITH DIAERESIS
> 
> I'm not sure what you mean by this. Do mean I use one of these
> accidentially? Or should I switch to one of these in my sitecutsomize.py?
> 
> I'm a bit confused. When I let Python print an � (umlaut a) by simply
> entering the 1-char string "�", it prints '\x84'.

In the encoding iso-8859-1, the character chr(0xe4) is LATIN SMALL
LETTER A WITH DIAERESIS.  chr(0x84) is not a printable character.

In the encodings I named above, chr(0x84) is LATIN SMALL LETTER A WITH
DIAERESIS.

Now, consider this program that creates a program:
    def maker(filename, encoding, ch):
        f = open(filename, "w")
        f.write("# -*- coding: %s -*-\n" % encoding)
        f.write("print '%s'\n" % ch)
if you call
    maker("coded.py", "iso-8859-1", "\xe4")
the created script will contain a byte string literal with the byte
'\xe4' in it.  When you run the script, it will print that byte followed
by the byte '\n'.  *In fact, this behavior (sequence of bytes written to
sys.stdout) doesn't depend on encoding, as long as
    '\xe4'.decode(encoding).encode(encoding) == '\xe4'
which should hold true in almost all single-byte encodings.*

What you *see* when you run the script depends on the meaning your
terminal window ("DOS box") assigns to the byte sequence '\xe4\n'.  On
mine, which expects output in UTF-8, I get a mark which indicates an
incomplete multi-byte character and then a newline.  On yours, you
apparently get some other character, possibly LATIN SMALL LETTER O WITH
TILDE if your terminal uses cp770, cp850, or cp857.

Now, consider this program with a u''-string literal:
    def umaker(filename, encoding, ch):
        f = open(filename, "w")
        f.write("# -*- coding: %s -*-\n" % encoding)
        f.write("print u'%s'\n" % ch)
If you call
    umaker("ucoded.py", "iso-8859-1", "\xe4")
the created script will again contain the literal byte "\xe4".  When you
run the script, you may get an error that says
    UnicodeError: ASCII encoding error: ordinal not in range(128)
this is because the string to be printed is a unicode string containing
the letter LATIN SMALL LETTER A WITH DIAERESIS, but Python believes the
terminal can only accept ASCII-encoded strings for display.  In my
Python 2.3 on Unix, sys.stdout.encoding is "UTF-8", and running
ucoded.py outputs the 3 byte sequence "\303\244\n", which in UTF-8 is a
LATIN SMALL LETTER A WITH DIAERESIS followed by a carriage return.

I suspect that wxpython is like tkinter: It is designed so that
u''-strings (unicode strings) can be given as arguments anywhere strings
can, and that internally the necessary steps are taken to find the
proper glyphs in the font to display that string.  Otherwise, there may
be a particular encoding assumed for all byte strings, which will have
no relationship to the -*- coding -*- of your scripts.

Jeff
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