Ad hoc lists vs ad hoc tuples

[Terry Reedy]

On 1/27/2010 12:32 PM, Antoine Pitrou wrote:
> Le Wed, 27 Jan 2010 02:20:53 -0800, Floris Bruynooghe a écrit :
>>
>> Is a list or tuple better or more efficient in these situations?
>
> Tuples are faster to allocate (they are allocated in one single step) and
> quite a bit smaller too.
> In some situations, in Python 2.7 and 3.1, they can also be ignored by
> the garbage collector, yielding faster collections.
>
> (not to mention that they are hashable, which can be useful)

Constant tuples (a tuple whose members are all seen as constants by the 
compiler) are now pre-compiled and constructed once and put into the 
code object as such rather than re-constructed with each run of the code.

 >>> from dis import dis
 >>> def l(): return [1,2,3]

 >>> def t(): return 1,2,3

 >>> dis(l)
   1           0 LOAD_CONST               1 (1)
               3 LOAD_CONST               2 (2)
               6 LOAD_CONST               3 (3)
               9 BUILD_LIST               3
              12 RETURN_VALUE
 >>> dis(t)
   1           0 LOAD_CONST               4 ((1, 2, 3))
               3 RETURN_VALUE
 >>> # 3.1

Terry Jan Reedy