On Sat, Jan 26, 2019 at 10:43 AM David Mertz <me...@gnosis.cx> wrote:
> No. It's simpler than that! Functions return a single value, period. > > That single value might happen to be a tuple or something else unpackable. > d'uh -- I was thinking common use case. > This makes it feel like we have multiple return values, but we never > actually do. The fact that "tuples are spelled by commas not by > parentheses" makes this distinction easy to ignore most of the time. > yup. And unpacking behavior. So I guess the correct way to phrase that is that functions return a single object, and that object may or may not be unpackable. Key to this is that unlike function parameters, python isn't doing anything special when returning a value form a function, or when assigning a value to a name: * functions return a value * assignment applies unpacking when assigning to multiple names. These two things are orthogonal in the language. The challenge in this case is that when you assign to a single name, there is no unpacking: x = 3, So in this case, the 1-tuple doesn't get unpacked -- when you are assigning to a single name, there is no unpacking to be done. but you can unpack a one-tuple, by assigning to name with a trailing comma: In [62]: x, = (3,) In [63]: x Out[63]: 3 So the challenge is that to support this new feature, we'd need to changing assignment, so that: x = an_object would look at an_object, and determine if it was one of these function_return_objects that should have the first value unpacked if assigned to a single name, but unpack the others if assigned to a tuple of names -- and THAT is a pretty big change! And it would still create odd behavior if teh function return value were not assigned right away, but stored in some other container: a_list = [fun1(), fun2()] So really, there is no way to create this functionality without major changes to the language. -CHB -CHB -- Christopher Barker, PhD Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython
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