On Thu, Nov 14, 2019 at 8:48 AM Eric Fahlgren <ericfahlg...@gmail.com> wrote: > I have used 'with' for so long that I was under the impression that the > as-target was just a name as in MRAB's simplified syntax above, so imagine my > surprise when I tried putting parentheses around the target and didn't get a > syntax error straight away. I of course had to explore a bit, and came up > with this. The ugly formatting of the with is simply to show that the parens > behave as expected. > class opener: > def __init__(self, *files): > self.files = [open(file) for file in files] > def __enter__(self): > return [file.__enter__() for file in self.files] > def __exit__(self, *exc_info): > for file in self.files: > file.__exit__(*exc_info) > return True > > with opener( > 'x', 'y', 'z' > ) as ( > f1, f2, f3 > ): > print(f1) > print(f1.closed) > print(f2) > print(f3) > > print(f1.closed)
Note that the semantics here are NOT the same as the semantics of either ExitStack or a single large 'with' statement. (And I'm not sure whether or not those two are the same.) With your opener, you first open each file, then enter each file; and only then are you considered to be inside the context. With a large 'with' statement, they should (I believe) be opened and entered individually. If one of the files fails to open, your constructor will fail, and self.files won't be set - you won't exit each of the files that you *did* open. ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/RT3RFVV7KRZ2Z6G2CI3GLHCFLTDUS6DG/ Code of Conduct: http://python.org/psf/codeofconduct/
