[Python-Dev] removing nested tuple function parameters (original) (raw)

Guido van Rossum guido at python.org
Mon Sep 19 19:21:28 CEST 2005

On 9/19/05, Terry Reedy <tjreedy at udel.edu> wrote:

I consider the current situation to be a consistency feature. To a first approximation, Python function calls 'pass' objects by name-binding: paramnamelist = argobjectlist Disabling structure unpacking in this assignment would make the language slightly more complex. Someone else posted the same observation in c.l.p.

Maybe, but there are enough differences between parameter/argument lists and sequences that this consistency sounds rather foolish to me. In fact, the feature came from a similar feature in ABC, but in ABC, parameter lists were considered assignment targets -- the outer level of parentheses was just a special case of tuple unpacking. Not so in Python, which has keyword parameters, *varargs, **keywords, and where f(x,) is the same as f(x) -- even though (x,) is a tuple and (x) is not.

Also, I bet many people will be surprised to know that this code doesn't work:

add = lambda (x, y): x+y print add(1, 2)

Another thought. By directly unpacking and not naming a sequence, one 'announces' that only the components are of interest and that nothing will be done with the sequence object itself.

Fair enough, though I'm not sure what use we can make of that information.

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

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