object.enable() anti-pattern

[MRAB]

On 09/05/2013 19:21, Steven D'Aprano wrote:
> On Thu, 09 May 2013 09:07:42 -0400, Roy Smith wrote:
>
>> In article <518b32ef$0$11120$c3e8da3 at news.astraweb.com>,
>>  Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:
>>
>>> There is no sensible use-case for creating a file without opening it.
>>
>> Sure there is.  Sometimes just creating the name in the file system is
>> all you want to do.  That's why, for example, the unix "touch" command
>> exists.
>
> Since I neglected to make it clear above that I was still talking about
> file objects, rather than files on disk, I take responsibility for this
> misunderstanding. I thought that since I kept talking about file
> *objects* and *constructors*, people would understand that I was talking
> about in-memory objects rather than on-disk files. Mea culpa.
>
> So, let me rephrase that sentence, and hopefully clear up any further
> misunderstandings.
>
> There is no sensible use-case for creating a file OBJECT unless it
> initially wraps an open file pointer.
>
You might want to do this:

f = File(path)
if f.exists():
     ...

This would be an alternative to:

if os.path.exists(path):
     ...

> This principle doesn't just apply to OOP languages. The standard C I/O
> library doesn't support creating a file descriptor unless it is a file
> descriptor to an open file. open() has the semantics:
>
> "It shall create an open file description that refers to a file and a
> file descriptor that refers to that open file description."
>
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html
>
> and there is no corresponding function to create a *closed* file
> description. (Because such a thing would be pointless.)
>
[snip]