[Python-3000] PEP 3113 (Removal of Tuple Parameter Unpacking) (original) (raw)

Guido van Rossum guido at python.org
Sun Mar 4 22:00:14 CET 2007

On 3/4/07, Ka-Ping Yee <python at zesty.ca> wrote:

On Fri, 2 Mar 2007, Brett Cannon wrote: > the removal of the automatic unpacking of sequence > arguments when a tuple parameter is present in a function's signature > (e.g., the (b, c) in def fxn(a, (b, c), d): pass).

As I think most people know by now, it makes me quite sad to see these going away. This is one of those really nice flexibilities in Python that makes Python Python (kind of like for/else). Brett's arguments for making them go (in my opinion) say little about the feature itself; most are merely observations that other parts of the language implementation fail to fully support this feature. For example, the "Introspection Issues" argument is mostly irrelevant: we are discussing a new incompatible version of the Python language, so it doesn't make sense to argue based on shortcomings of previous versions. The weakness is in the introspection capabilities. (It's difficult to introspect inside local scopes -- of course that does not mean we should remove local scopes from the language). Similarly, the complaints about poor error messages are irrelevant. If the error messages are inadequate, simply fix them. "Exception to the Rule" is also about other features that don't support tuple parameters, not about tuple parameters themselves. If these features are incomplete, they can be completed. "No Loss of Abilities If Removed" is not an argument to remove anything; it's a neutral claim that removing it won't hurt. All for/else loops could be easily rewritten with a break flag instead and no functionality would be lost -- but functionality is not the question; the expressiveness of the language suffers. In summary, all of the arguments for removing this feature are of the form "It won't hurt very much if we remove the feature"; the arguments for keeping the feature are of the form "This feature is useful and good for the language." Notice the asymmetry: there are no arguments that removing it will actually yield a better language, only arguments that the harm caused by removing it will be small.

I don't see the feature useful for the language. It's a wart that startles most experienced users they first come across it. In order to make room for new features we need to make the language smaller. This cut is one of the least controversial cuts imaginable (your opposition notwithstanding).

You'll get over your sadness.

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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