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Why exception from os.path.exists()?


On 07-06-18 11:29, Marko Rauhamaa wrote:
> Antoon Pardon <antoon.pardon at vub.be>:
>
>> On 07-06-18 05:55, Steven D'Aprano wrote:
>>> As a Python programmer, how does treating NUL specially make our life
>>> better?
>> By treating possible path values differently from impossible path
>> values.
> There are all kinds of impossibility. The os.stat() reports those
> impossibilities via an OSError exception. It's just that
> os.path.exists() converts the OSError exception into a False return
> value. A ValueError is raised by the Python os.stat() wrapper to
> indicate that it can't even deliver the request to the kernel.
>
> The application programmer doesn't give an iota who determined the
> impossibility of a pathname.

So? The fact that the application programmer doesn't give an iota who
determined the impossibility of a pathname, doesn't imply he is
equally unconcerned about the specific impossibility he ran into.

> Unfortunately, os.path.exists() forces the
> distinction on the application.

No it doesn't. It forces the distinction between two different kinds
of impossibilities, but you don't have to care where they originate
from.

>  If I have to be prepared to catch a
> ValueError from os.path.exists(), what added value does os.path.exists()
> give on top of os.stat()? The whole point of os.path.exists() is
>
>   1. To provide an operating-system-independent abstraction.
>
>   2. To provide a boolean interface instead of an exception interface.

Mayby trying to provide such an interface is inherently flawed. Answering
me a path doesn't exist because of a permission problem is IMO not a good
idea.

--
Antoon.