On Wed, May 22, 2019 at 7:32 PM Yanghao Hua <yanghao...@gmail.com> wrote: > The .next could have been saved by using python descriptors but now > you have to type something like "obj.signal = 5" instead of "signal = > 5", and it does not work if you want a local signal, where signal = 5 > will always make signal to be 5, instead of feeding 5 into this > signal.
Redefining assignment based on the data type of the left hand side is fraught with peril. Various languages have it, or something like it, and it can VERY quickly become a source of nightmare bugs. > I have experimented by adding two new python operators, left arrow: <- > and right arrow ->, which users can define their behaviors. and it > still looks like kind of the non-blocking assignment operators in > hardware description languages (e.g. verilog <=). Also it could be > used to build data flows like a -> b -> c -> d -> ... Bear in mind that the <- operator can also be interpreted as a < comparison and - unary negation. >>> x = 0 >>> x <- 1 False >>> x = -2 >>> x <- 1 True > Another side effect is this "__arrow__" call can fully replace > descriptors and allow you to generate descriptor-like behavior on > object initialization time instead of class definition time, e.g. in > __init__(self,...) to dynamically create self.abc like fields which > can be then accessed like obj.abc <- 3 etc. This currently with > descriptors can only be achieved elegantly by using meta classes. If you want an operator to (ab)use for this kind of thing, I would recommend << and >>, implemented with __lshift__ and __rshift__ (and their corresponding reflected forms). After all, you'd be following in the footsteps of C++, and as we all know, C++ is a bastion of elegant language design with no strange edge cases at all! :) > This is the first time I am writing to python-ideas list, just want to > hear what you guys think, should python actually allow operators to be > first class citizens? does the arrow operator makes sense at all? Any > other better ways to redefine the "assignment" behavior by user? Your post doesn't really say much about first-class operators. You suggested two things (allowing assignment to be redefined, and the arrow operators), but I'm not sure what you actually mean by operators being first-class citizens. https://en.wikipedia.org/wiki/First-class_citizen To be first-class citizens, operators would have to be able to be passed to functions - for instance: def frob(x, y, oper): return x oper y assert frob(10, 20, +) == 30 assert frob(10, 20, *) == 200 The nearest Python currently has to this is the "operator" module, in which you'll find function versions of the operators: def frob(x, y, oper): return oper(x, y) assert frob(10, 20, operator.add) == 30 assert frob(10, 20, operator.mul) == 200 Is this what you're talking about? ChrisA _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
