[Python-3000] Set literals - another try (original) (raw)

Josiah Carlson jcarlson at uci.edu
Tue Aug 8 22:21:39 CEST 2006

"Collin Winter" <collinw at gmail.com> wrote:

On 8/8/06, Josiah Carlson <jcarlson at uci.edu> wrote: > I personally don't see much of a use for set literals, considering that > there is a non-ambiguous spelling of it currently; set(...), whose only > cost above and beyond that of a set literal is a global name lookup. I thought one of the main arguments in favor of set literals is that a literal form would allow the compiler to perform optimisations that the set(...) spelling doesn't allow.

The optimization argument used to define language syntax seems a bit like the "tail wagging the dog" cliche. For immutable literals that are used a huge number of times (int, tuple, and other immutables), a literal syntax for compiler optimization makes sense. But for mutables (list, dict, etc.), literal syntax is more a convenience as than an optimization, as the compiler hasn't historically created once and copied for re-use, but pushed values on the stack and called the relevant create list bytecode. [1]

[1] Python 2.4.3 (#69, Mar 29 2006, 17:35:34) [MSC v.1310 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information.

import dis def foo(): ... return [1,2,3] ... def goo(): ... return (1,2,3) ... dis.dis(foo) 2 0 LOAD_CONST 1 (1) 3 LOAD_CONST 2 (2) 6 LOAD_CONST 3 (3) 9 BUILD_LIST 3 12 RETURN_VALUE dis.dis(goo) 2 0 LOAD_CONST 4 ((1, 2, 3)) 3 RETURN_VALUE

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