[Python-Dev] Python-3.0, unicode, and os.environ

[Toshio Kuratomi]

Adam Olsen wrote:
> On Thu, Dec 4, 2008 at 1:02 PM, Toshio Kuratomi <a.badger at gmail.com> wrote:
>> I opened up bug http://bugs.python.org/issue4006 a while ago and it was
>> suggested in the report that it's not a bug but a feature and so I
>> should come here to see about getting the feature changed :-)
>>
>> I have a specific problem with os.environ and a somewhat less important
>> architectural issue with the unicode/bytes handling in certain os.*
>> modules.  I'll start with the important one:
>>
>> Currently in python3 there's no way to get at environment variables that
>> are not encoded in the system default encoding.  My understanding is
>> that this isn't a problem on Windows systems but on *nix this is a huge
>> problem.  environment variables on *nix are a sequence of non-null
>> bytes.  These bytes are almost always "characters" but they do not have
>> to be.  Further, there is nothing that requires that the characters be
>> in the same encoding; some of the characters could be in the UTF-8
>> character set while others are in latin-1, shift-jis, or big-5.
> 
> Multiple encoding environments are best described as "batshit insane".
>  It's impossible to handle any of it correctly *as text*, which is why
> UTF-8 is becoming a universal standard.  For everybody's sanity python
> should continue to push it.
> 
Amen brother!

> However, some pragmatism is also possible.

Unfortunately, this is exactly what I'm talking about :-)

>  Many uses of PATH may
> allow it to be treated as black-box bytes, rather than text.  The
> minimal solution I see is to make os.getenv() and os.putenv() switch
> to byte modes when given byte arguments, as os.listdir() does.  This
> use case doesn't require the ability to iterate over all environment
> variables, as os.environb would allow.
> 
This would be a partial implementation of my option #3.  It allows the
programmer to workaround problems but does allow subtle bugs to creep in
unawares.  For instance::

> I do wonder if controlling the environment given to a subprocess
> requires os.environb, but it may be too obscure to really matter.
> 
If you wanted to change one variable before passing it on to the
subprocess this could lead to head-scratcher bugs.  Here's a contrived
example:  Say I have an app that talks to multiple cvs repositories.  It
copies os.environ and modifies CVSROOT and CVS_RSH then calls subprocess
with env=temp_env.  If the PATH variable contains non-decodable elements
on some machines, this could lead to mysterious failures.  This is
particularly bad because we aren't directly modifying PATH anywhere in
our code so there won't be an obvious reason in the code that this is
failing.

-Toshio

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