[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Why exception from os.path.exists()?

On Tue, Jun 5, 2018 at 5:37 PM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
> On Mon, 04 Jun 2018 22:13:47 +0200, Peter J. Holzer wrote:
>> On 2018-06-04 13:23:59 +0000, Steven D'Aprano wrote:
> [...]
>>> I don't know whether or not the Linux OS is capable of accessing files
>>> with embedded NULs in the file name. But Mac OS is capable of doing so,
>>> so it should be possible. Wikipedia says:
>>> "HFS Plus mandates support for an escape sequence to allow arbitrary
>>> Unicode. Users of older software might see the escape sequences instead
>>> of the desired characters."
>> I don't know about MacOS. In Linux there is no way to pass a filename
>> with an embedded '\0' (or a '/' which is not path separator) between the
>> kernel and user space. So if a filesystem contained such a filename, the
>> kernel would have to map it (via an escape sequence or some other
>> mechanism) to a different file name. Which of course means that - from
>> the perspective of any user space process - the filename doesn't contain
>> a '\0' or '/'.
> That's an invalid analogy. According to that analogy, Python strings
> don't contain ASCII NULs, because you have to use an escape mechanism to
> insert them:
>     string = "Is this \0 not a NULL?"
> But we know that Python strings are not NUL-terminated and can contain
> NUL. It's just another character.

No; by that analogy, a Python string cannot contain a non-Unicode
character. Here's a challenge: create a Python string that contains a
character that isn't part of the Universal Character Set.