On Wed, May 25, 2016 at 01:11:35PM +0000, Michael Selik wrote:
py> mapping = {"a": 1, "b": 2, "c": 3} py> {"a": x, "b": y, "c": z} = mapping py> x, y, z (1, 2, 3)
I think that is too verbose and visually baffling. I'd rather see something less general and (in my opinion) more useful: a, b, c = **mapping being equivalent to: a = mapping['a'] b = mapping['b'] c = mapping['c'] It's less general, because you can only use the same names as the keys in the dict. But most of the time you'll probably want to do that anyway. Think of (for example) carrying around a "settings" or "preferences" dict: prefs = {'width': 80, 'height': 200, 'verbose': False, 'mode': PLAIN, 'name': 'Fnord', 'flags': spam|eggs|cheese, ... } # plus many more keys:values There's no need to unpack the entire dict, you can grab only the keys you need: width, height = **prefs # like width = prefs['width'] height = prefs['height'] Sure, you are forced to use the same variable names as the keys, but that's what you will probably do most of the time. You're not likely to write: foo = prefs['width'] bar = prefs['height'] although you might write: zip_code = prefs['zip code'] but probably shouldn't. (Just use 'zip_code' as the key.) Another awkward case is when a key is a keyword: except_ = prefs['except'] but I expect those cases will be relatively rare, and you can always manually unpack them the old fashioned way. Admittedly your syntax would allow those cases, at the cost of a more verbose statement: {'width': foo, 'height': bar, 'except': except_, 'zip code': zip_code} = mapping but I think that's mostly an over-generalisation and too hard to grasp what is going on. Naturally the order of the keys doesn't matter: mode, height, width = **prefs height, mode, width = **prefs etc are all the same. If you twist my arm and force me to come up with syntax for a "change of variable name", I'd consider: height, width, zip_code:'zip code', except_:'except' = **mapping In other words, if the target on the left is a plain name, the unpacking does: name = mapping['name'] If the target on the left has a colon, it is an identifier followed by key. The identifier can be any valid reference, including dots and [] subscripts. The key must be a string: identifier:'key' which performs: identifier = mapping['key'] Examples of valid colon targets: spam:'ham' # like spam = mapping['ham'] spam[1].eggs:'while' # like spam[1].eggs = mapping['while'] etc. If there's too many targets to comfortably fit on the one line, wrap them in parentheses to allow line wrapping: (height, flags, except_:'except', mymodule.obj.attribute[2].gamma:'gamma', alpha) = **prefs But the simple case, the case you'll use most of the time, is simple: height, width, verbose, flags = **prefs -- Steve