On 7/19/2017 12:10 PM, Giampaolo Rodola' wrote:
On Wed, Jul 19, 2017 at 5:20 PM, Tim Peters
<tim.pet...@gmail.com
<mailto:tim.pet...@gmail.com>> wrote:
[Giampaolo Rodola' <g.rod...@gmail.com
<mailto:g.rod...@gmail.com>>]
> Still much slower (-4.3x) than plain tuples though:
>
> $ python3.7 -m timeit -s "import collections; Point => collections.namedtuple('Point',
('x', 'y'));" "Point(5, 11)"
> 1000000 loops, best of 5: 313 nsec per loop
>
> $ python3.7 -m timeit "tuple((5, 11))"
> 5000000 loops, best of 5: 71.4 nsec per loop
I believe this was pointed out earlier: in the second case,
1. (5, 11) is built at _compile_ time, so at runtime it's only
measuring a LOAD_FAST to fetch it from the code's constants block.
2. The tuple() constructor does close to nothing when passed a tuple:
it just increments the argument's reference count and returns it.
>>> t = (1, 2)
>>> tuple(t) is t
True
In other words, the second case isn't measuring tuple _creation_ time
in any sense: it's just measuring how long it takes to look up the
name "tuple" and increment the refcount on a tuple that was created at
compile time.
Oh right, I didn't realize that, sorry. Should have been something like
this instead:
$ python3.7 -m timeit -s "import collections; Point =
collections.namedtuple('Point', ('x', 'y')); x = [5, 1]" "Point(*x)"
1000000 loops, best of 5: 311 nsec per loop
$ python3.7 -m timeit -s "x = [5, 1]" "tuple(x)"
5000000 loops, best of 5: 89.8 nsec per loop
I thing "x,y = 5, 1" in the setup and "Point(x,y)", and "(x,y)" better
model real situations. "x,y" cannot be optimized away but reflects how
people would construct a tuple given x and y.
On my Win10 machine with 3.7 with debug win32 build (half as fast as
without debug), I get
F:\dev\3x>python -m timeit -s "import collections as c; Point =
c.namedtuple('Point',('x','y')); x,y=5,1", "Point(x,y)"
200000 loops, best of 5: 1.86 usec per loop
F:\dev\3x>python -m timeit -s "x,y=5,1", "(x,y)"
2000000 loops, best of 5: 156 nsec per loop
If one starts with a tuple, then the Point call is pure extra overhead.
If one does start with a list, I get 1.85 usec and 419 nsec
--
Giampaolo - http://grodola.blogspot.com
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--
Terry Jan Reedy
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