On Fri, Jul 29, 2016 at 7:34 PM, Terry Reedy <tjre...@udel.edu> wrote: > On 7/29/2016 7:59 AM, eryk sun wrote: >> >> On Fri, Jul 29, 2016 at 8:43 AM, Antoon Pardon >> <antoon.par...@rece.vub.ac.be> wrote: >>> >>> The problem seems to come from my expectation that a file >>> is its own iterator and in python3 that is no longer true >>> for a NamedTemporaryFile. >> >> For some reason it uses a generator function for __iter__ > > This is a common idiom for having iterable.__iter__ return an iterator > without writing and instanciating an iterator class.
Yes, using a generator function is a simple way to create multiple iterators of an iterable, which is especially useful for a sequence that's independently reiterable. However a Python io file is its own iterator because it's based on a synchronous operating system File that maintains a file pointer. (Python io files don't support Windows asynchronous file access, which doesn't update the File pointer, and even the low-level _winapi and _overlapped implementations don't support this.) In this case there's no point that I can see in using a generator function for __iter__. If you call iter() again on the tempfile._TemporaryFileWrapper, it doesn't produce a new iteration of the underlying file until seek(0) is called to reset the file pointer. So __iter__ may as well return `self` and have __next__ proxy next(self.file). -- https://mail.python.org/mailman/listinfo/python-list