strange interaction between open and cwd

[Baz Walter]

On 03/05/10 19:12, Grant Edwards wrote:
> On 2010-05-03, Baz Walter<bazwal at ftml.net>  wrote:
>
>>> You requested something that wasn't possible.  It failed.  What do
>>> you think should have happened?
>>
>> path = '../abc.txt'
>>
>> os.path.realpath(path) ->  "OSError: [Errno 2] No such file or directory"
>>
>> therefore:
>>
>> open(path) ->  "IOError: [Errno 2] No such file or directory"
>>
>> i think that if the first of these seemingly "impossible" requests
>> fails, it is reasonable to expect that the second one also fails. but
>> the second one (sometimes) doesn't.
>
> Because the second one isn't impossible in the case you posted.
 >
>> i think they should always either both succeed, or both fail.
>
> That's not how Unix filesystems work.
>
> Are you saying that Python should add code to it's open() builtin
> which calls realpath() and then refuses to open files for which
> realpath() fails?

my original question was really about *how* python does the "seemingly 
impossible". i had hoped there might be a way to augment realpath so 
that it would always work for any path which is openable. but apparently 
that is not possible for unix filesystems.

 > Even though the user provided a legal and openable path?

that sounds like an operational definition to me: what's the difference 
between "legal" and "openable"?