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To: python-list@python.org
From: Peter Otten <__peter__@web.de>
Subject: Re: sys.argv as a list of bytes
Date: Wed, 18 Jan 2012 15:01:38 +0100
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Olive wrote:

> On Wed, 18 Jan 2012 09:05:42 +0100
> Peter Otten <__peter__@web.de> wrote:
> 
>> Olive wrote:
>> 
>> > In Unix the operating system pass argument as a list of C strings.
>> > But C strings does corresponds to the bytes notions of Python3. Is
>> > it possible to have sys.argv as a list of bytes ? What happens if I
>> > pass to a program an argumpent containing funny "character", for
>> > example (with a bash shell)?
>> > 
>> > python -i ./test.py $'\x01'$'\x05'$'\xFF'
>> 
>> Python has a special errorhandler, "surrogateescape" to deal with
>> bytes that are not valid UTF-8. If you try to print such a string you
>> get an error:
>> 
>> $ python3 -c'import sys; print(repr(sys.argv[1]))'
>> $'\x01'$'\x05'$'\xFF' '\x01\x05\udcff'
>> $ python3 -c'import sys; print(sys.argv[1])' $'\x01'$'\x05'$'\xFF'
>> Traceback (most recent call last):
>>   File "<string>", line 1, in <module>
>> UnicodeEncodeError: 'utf-8' codec can't encode character '\udcff' in
>> position 2: surrogates not allowed
>> 
>> It is still possible to get the original bytes:
>> 
>> $ python3 -c'import sys; print(sys.argv[1].encode("utf-8",
>> "surrogateescape"))' $'\x01'$'\x05'$'\xFF' b'\x01\x05\xff'
>> 
>> 
> 
> But is it safe even if the locale is not UTF-8? I would like to be able
> to pass a file name to a script. I can use bytes for file names in the
> open function. If I keep the filename as bytes everywhere it will work
> reliably whatever the locale or strange character the file name may
> contain.

I believe you need not convert back to bytes explicitly, you can open the 
file with open(sys.argv[i]). I don't know if there are cornercases where 
that won't work; maybe http://www.python.org/dev/peps/pep-0383/ can help you 
figure it out.