On Friday, March 2, 2018 at 10:05:41 AM UTC+5:30, Steven D'Aprano wrote: > On Thu, 01 Mar 2018 16:26:47 -0800, ooomzay wrote: > > >> >> When does the destination file get closed? > >> > > >> > When you execute:- > >> > > >> > del dst > >> > > >> > or:- > >> > > >> > dst = something_else > >> > >> What if you don't? > > > > Then the resource will remain open until your script exits at which > > point it is probably not very well defined exactly when or even if the > > destructor/__del__ will be called. > > > > I.e. Don't do this! Did you have some realistic case in mind or are you > > just probing the behaviour? > > > If you're going to *require* the programmer to explicitly del the > reference: > > f = open("file") > text = f.read() > del f > > then you might as well require them to explicitly close the file: > > f = open("file") > text = f.read() > f.close() > > which we know from many years experience is not satisfactory except for > the simplest scripts that don't need to care about resource management. > > That's the fatal flaw in RAII: for resources that you care about their > *timely* release, the problem is that the lifespan of the resource may > not be the same as the lifetime of the object. Especially for files, the > problem is that the lifespan of resource (the time you are actually using > it) may be significantly less than the lifespan of the object holding > onto that resource. Since there's no way for the interpreter to know > whether or not you have finished with the resource, you have a choice: > > - close the resource yourself (either explicitly with file.close(), > or implicitly with a context manager); > > - or keep the resource open indefinitely, until such eventual time > that the object is garbage collected and the resource closed.
Please excuse if this has been addressed above and/or its too basic: What's the difference between RAII and python's with/context-managers? -- https://mail.python.org/mailman/listinfo/python-list