On Fri, 15 Nov 2019 at 22:54, Chris Angelico <ros...@gmail.com> wrote:
>
> On Sat, Nov 16, 2019 at 9:44 AM Oscar Benjamin
> <oscar.j.benja...@gmail.com> wrote:
> >
> > On Fri, 15 Nov 2019 at 12:04, Serhiy Storchaka <storch...@gmail.com> wrote:
> > >
> > > 15.11.19 12:40, Jonathan Fine пише:
> > > > The original poster wanted, inside 'with' context management, to open
> > > > several files. Context management is, roughly speaking, deferred
> > > > execution wrapped in a try ... except .... statement.
> > >
> > > In case of open() there is no deferred execution. The resource is
> > > acquired in open(), not in __enter__().
> >
> > I've often thought that this was the root of various awkwardnesses
> > with context managers. Ideally a well-behaved context manager would
> > only use __exit__ to clean up after __enter__ but open doesn't do
> > that. The nested context manager was designed for this type of
> > well-behaved context manager but was then considered harmful because
> > open (one of the most common context managers) misbehaves.
> >
> > Maybe some of these things could be simpler if it was clarified that a
> > context manager shouldn't acquire resource before __enter__ and a new
> > version of open was provided.
> >
>
> Hmm. What exactly is the object that you have prior to the file being
> opened? It can't simply be a File, because you need to specify
> parameters to the open() call. Is it a "file ready to be opened"?
> What's the identity of that?
Good question :)
Maybe it's an "opener":
class opener:
def __init__(self, *args):
self.args = args
def __enter__(self):
fileobj = self.fileobj = open(*self.args)
return self.fileobj
def __exit__(self, *args):
return self.fileobj
with opener('w.txt', 'w') as fout:
fout.write('asd\n'*10)
--
Oscar
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