[Python-Dev] Why does TemporaryDirectory not wait for `__enter__`?

[Antoine Pitrou]

On Sun, 27 Feb 2011 00:39:16 +1000
Nick Coghlan <ncoghlan at gmail.com> wrote:
> On Sat, Feb 26, 2011 at 10:52 PM, cool-RR <cool-rr at cool-rr.com> wrote:
> > Hello,
> > I noticed that the `TemporaryDirectory` context manager creates the folder
> > on `__init__` rather than on `__enter__`, resulting in complexity, bugs, and
> > hackarounds in `__del__`. I assume there's a good reason for this decision.
> > What is it?
> 
> >From the docstring: "This has the same behavior as mkdtemp but can be
> used as a context manager." Like files, it *can* be used as a context
> manager, but doesn't have to be.
> 
> Also, the complexity wouldn't go away even if the directory creation
> was delayed until the __enter__ invocation. People can still call
> __enter__ directly, so __del__ would still be obliged to try to clear
> things up as best it could.

Calling __enter__ directly without caring to call __exit__ afterwards
should certainly be considered a user bug (not to mention of dubious
utility in this case, since it's easier to spell mkdtemp() than
TemporaryDirectory().__enter__()).

Regards

Antoine.