On 2005-11-28, Duncan Booth <[EMAIL PROTECTED]> wrote: > Antoon Pardon wrote: > >>> >>> def func(x): >>> ... if x in [1,3,5,7,8]: >>> ... print 'x is really odd' >>> ... >>> >>> dis.dis(func) >>> ... >>> 3 20 LOAD_FAST 0 (x) >>> 23 LOAD_CONST 2 (1) >>> 26 LOAD_CONST 3 (3) >>> 29 LOAD_CONST 4 (5) >>> 32 LOAD_CONST 5 (7) >>> 35 LOAD_CONST 6 (8) >>> 38 BUILD_LIST 5 >>> 41 COMPARE_OP 6 (in) >> >> I'm probably missing something, but what would be the problem if this >> list was created during compile time? > > Not much in this particular instance. 'x in aList' is implemented as > aList.__contains__(x), so there isn't any easy way to get hold of the > list[*] and keep a reference to it. On the other hand: > > def func(x): > return x + [1, 3, 5, 7, 8] > > we could pass in an object x with an add operator which gets hold of its > right hand operand and mutates it. > > So the problem is that we can't just turn any list used as a constant into > a constant list, we need to be absolutely sure that the list is used only > in a few very restricted circumstances, and since there isn't actually any > benefit to using a list here rather than a tuple it hardly seems > worthwhile.
The question is, should we consider this a problem. Personnaly, I see this as not very different from functions with a list as a default argument. In that case we often have a list used as a constant too. Yet python doesn't has a problem with mutating this list so that on the next call a 'different' list is the default. So if mutating a list used as a constant is not a problem there, why should it be a problem in your example? -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
