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From: eryk sun <eryksun@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: TypeError: '_TemporaryFileWrapper' object is not an iterator
Date: Fri, 29 Jul 2016 11:59:52 +0000
Lines: 37
Message-ID: <mailman.22.1469793641.6033.python-list@python.org>
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On Fri, Jul 29, 2016 at 8:43 AM, Antoon Pardon
<antoon.pardon@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__ instead of
returning self, which would allow it to proxy the wrapped file's
__next__ method. There may be a good reason for that design decision,
but at the moment I don't see it, so I'd simply try the following:

    import tempfile
    import functools

    class _TemporaryFileWrapper(tempfile._TemporaryFileWrapper):
        def __iter__(self):
            return self
        def __next__(self):
            return next(self.file)

    @functools.wraps(tempfile.NamedTemporaryFile, assigned=['__doc__'])
    def NamedTemporaryFile(*args, **kwds):
        f = tempfile.NamedTemporaryFile(*args, **kwds)
        f.__class__ = _TemporaryFileWrapper
        return f

    if __name__ == '__main__':
        with NamedTemporaryFile('w+', prefix='tmptest-') as f:
            for n in range(10):
                f.write('This is line %d.\n' % n)
            f.seek(0)
            try:
                while True:
                    print(next(f), end='')
            except StopIteration:
                pass