Developer Forum

One thing I ofter wonder is which is better when you just need a
throwaway sequence: a list or a tuple? E.g.:

if foo in ['some', 'random', 'strings']:
...
if [bool1, bool2, boo3].count(True) != 1:
...

(The last one only works with tuples since python 2.6)

Is a list or tuple better or more efficient in these situations?


Regards
Floris

PS: This is inspired by some of the space-efficiency comments from the
list.pop(0) discussion.

On Jan 27, 10:20m, Floris Bruynooghe < XXXX@XXXXX.COM >

> ...> > if [bool1, bool2, boo3].count(True) != 1:> > >. >>
> (The last one only works with tuples since python 2.>) >>
> Is a list or tuple better or more efficient in these situation>? >>
> Regar>s
> Flor>s >>
> PS: This is inspired by some of the space-efficiency comments from t>e
> list.pop(0) discussion.

I tend to use tuples unless using a list makes it easier to read. For
example:

if foo in ('some', 'random', 'strings'):

draw.text((10,30), "WHICH IS WHITE", font=font)
draw.line([(70,25), (85,25), (105,45)])

I've no idea what the performance difference is; I've always assumed
it's negligible.

Iain

Tuples are a faster to create than lists, so if you create
lots of them and don't need the list features, use tuples.

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The fact that you have felt able to neglect the performance difference
makes it quite literally negligible.

regards
Steve
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The fact that you have felt able to neglect the performance difference
makes it quite literally negligible.

regards
Steve
--
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Le Wed, 27 Jan 2010 02:20:53 -0800, Floris Bruynooghe a crit:

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

Thanks for all the answers! This is what I was expecting but it's
nice to see it confirmed.

Regards
Floris

Sadly that's not entirely accurate.

Tuples whose members are all simple constants are pre-compiled, but here's
an example of a tuple whose members are all constants but doesn't get
optimised:

data = (
('hello', 42),
('world', 24),
)
return data

3 0 LOAD_CONST 5 (('hello', 42))

4 3 LOAD_CONST 6 (('world', 24))
6 BUILD_TUPLE 2
9 STORE_FAST 0 (data)

6 12 LOAD_FAST 0 (data)
15 RETURN_VALUE


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