At 06:15 PM 9/28/2005 +0200, Pierre Barbier de Reuille wrote: >Regularly, you see questions about augmented assignment on Python-tutor >mailing list, I often have question in my lab because of problems ... >most of the time people learn to avoid these operators in the end ! And >my look in the standard library confirmed my intuition about it.
Some example of the problems would help. For the specific bug report being discussed, I don't understand why someone would use augmented assignment with an immutable lvalue, since x |= y is short for x = x | y, which is clearly invalid on the face of it if x is a tuple member! >The problem is: this seems to be more a problem than a solution ! >There is a huge difference between in-place or not, and I find it very >difficult not to consider it. Consider string addition. The fact that string concatenation can be implemented with += allows a string to consider based on its refcount to return a new string or to modify itself in-place. If someone uses a = b + c, it may be assumed that they still desire a reference to b, and that therefore the operation *cannot* be done in-place. If they use a += b, then this is a *hint* that an in-place operation is desirable. So, there are two features of augmented assignment: 1. It is a shortcut for spelling out the full assignment 2. Types that override augmented assignment methods may optimize in-place operations, *without the need for client code to change*. >If you have a use-case for this "let the >object decide about in-place operation or not" I'd be interested as I >found none. The whole point of it is that I don't need to *care* whether a particular use is such or not. I simply say what the code intends, and then if somebody needs to pass in something different, or the behavior of some other part of the system changes, then I get that for free. Looking for a specific use case for that is like looking for a use case for duck typing. That is, *everything* is a use case for it, because the point isn't the initial state of the system. The point is what happens when you *change* the system. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
