On Thu, 26 Apr 2018 10:20:40 +1000 Chris Angelico <ros...@gmail.com> wrote: > On Thu, Apr 26, 2018 at 10:11 AM, Yury Selivanov > <yselivanov...@gmail.com> wrote: > > Just yesterday this snippet was used on python-dev to show how great the > > new syntax is: > > > > my_func(arg, buffer=(buf := [None]*get_size()), size=len(buf)) > > > > To my eye this is an anti-pattern. One line of code was saved, but the > > other line becomes less readable. The fact that 'buf' can be used after > > that line means that it will be harder for a reader to trace the origin of > > the variable, as a top-level "buf = " statement would be more visible. > > Making 'buf' more visible is ONLY a virtue if it's going to be used > elsewhere. Otherwise, the name 'buf' is an implementation detail of > the fact that this function wants both a buffer and a size. Should you > want to expand this out over more lines, you could do this: > > template = [None] > buf = template*get_size() > length = len(buf) > my_func(arg, buffer=buf, size=length) > > What are the names 'template' and 'length' achieving? Why should they > claim your attention?
What is the name 'buf' in the binding expression achieving? Why should it claim my attention? It's not any different: it's just something that's used in a statement then unnecessary. Yet it will persist until the end of the enclosing scope, being retained for no reason. Perhaps we need C-like nested scopes, if such is the concern about names that live for too long? (of course, the fact that `my_func` needs you to pass its argument's length as a separate argument, while it could compute it by itself, is a bit silly) As a side note, personally, I'm usually much more concerned about the lifetime of *values* than the lifetime of names. The latter are cheap, the former can represent expensive resources. Regards Antoine. > They are useless relics of a done-and-dusted > calculation, being retained for no reason. They do not deserve > top-level placement. > > The form as given above is starting to get a bit noisy, but I strongly > disagree that 'buf' deserves to be a stand-alone name. It is as > valueless as 'template' is. > > ChrisA _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
