[mjschultz]

I'm probably doing it wrong but I measured exactly this yesterday and the dict version was faster:

    $ python -m timeit --setup "from collections import namedtuple; Point = namedtuple('Point', ['x', 'y']); p = Point(x=0, y=0)" "p.x + p.y"
    1000000 loops, best of 3: 0.284 usec per loop

vs.

    $ python -m timeit --setup "p = {'x': 0, 'y': 0}" "p['x'] + p['y']"
    10000000 loops, best of 3: 0.0737 usec per loop

Maybe the use isn't right because I agree with your belief that namedtuple is suppose to be more performant.

[pdonis]

You should be creating a dict vs. a namedtuple instance once, then accessing it many, many times. What you're doing is creating a lot of dict vs. namedtuple instances, then accessing each one only once. That's mostly testing the instance creation time, not the field access time.

[mjschultz]

That code should only create the dict/namedtuple instance once, then access it many, many times.

The creation occurs in the --setup portion. The field accesses occur in the actual looping portion of the timeit code.

[pdonis]

Ah, ok, I see, for some reason my browser wasn't showing the namedtuple code snippet right. Now I need to go look at the namedtuple code to see why accessing the fields by name is slower than accessing them by index.

[the_mitsuhiko]

Yep. Because the dictionary literal gets created via opcodes in the interpreter loop whereas the named tuple pays the price of calling a function and setting up an interpreter frame.

[mjschultz]

The --setup code (creating the namedtuple and dict) is only executed once.

The timed portion is simply the field accesses.

[tterrace]

Here's a neat (and totally unpythonic) way to bring that down a bit:

    python -m timeit --setup "from collections import namedtuple; Point = namedtuple('Point', ['x', 'y']); p = Point(x=0, y=0); get_y = Point.y.fget; get_x = Point.x.fget" "get_x(p) + get_y(p)"

[mapleoin]

I think you're timing the import in there, too. Plus, creating an object of a class rather than using a literal will always be slower.

[mjschultz]

Does the --setup statement really get timed?

My reading of the docs[1] has always led me to believe that it doesn't. For example, "It is possible to provide a setup statement that is executed only once at the beginning"

[1]: http://docs.python.org/2/library/timeit.html

[vibragiel]

It doesn't get timed. You can quickly test this by adding an expensive operation to your setup and checking that it doesn't affect the resulting time.

[mapleoin]

Aaah, ok. I totally didn't read the --setup arg.