list addition methods compared.

[Steven Bethard]

Ishwor wrote:
> Could u run the code in your machine and perhaps and let me know what
> the average speed is??
> The code is -
[snip code not using timeit]


Are you aware of the timeit module?  It can do most of these timings for 
you.  Here's the code I used:

------------------------------ extend.py ------------------------------
def add(items):
     lst = []
     for item in items:
         lst = lst + [item]

def iadd(items):
     lst = []
     for item in items:
         lst += [item]

def extend(items):
     lst = []
     for item in items:
         lst.extend([item])

def extend_ext(items):
     lst = []
     ext = lst.extend
     for item in items:
         ext([item])

def append(items):
     lst = []
     for item in items:
         lst.append(item)

----------------------------------------------------------------------

and here's the commands I ran (using Python 2.4)[1]:

$ python -m timeit -s "import extend; items = range(10000)" 
"extend.add(items)"
10 loops, best of 3: 588 msec per loop

$ python -m timeit -s "import extend; items = range(10000)" 
"extend.iadd(items)"
100 loops, best of 3: 9.68 msec per loop

$ python -m timeit -s "import extend; items = range(10000)" 
"extend.extend(items)"
100 loops, best of 3: 11.5 msec per loop

$ python -m timeit -s "import extend; items = range(10000)" 
"extend.extend_ext(items)"
100 loops, best of 3: 9.09 msec per loop

$ python -m timeit -s "import extend; items = range(10000)" 
"extend.append(items)"
100 loops, best of 3: 4.5 msec per loop

A few things worth noting:

(1) I didn't see the top of this thread, but I'm assuming that you've 
got a conditional or something in your real loop or you could just use 
lst.extend(items) without ever iterating over the items list.  Your real 
code may actually require extend-style functionality, but as the results 
above show, if you really only have one item to add, list.append is 
definitely the better way to go.

(2) Yes, using += is slightly faster than list.extend, but only because 
"lst.extend" requires an extra attribute lookup.  If you factor that out 
(like I did with the line "ext = lst.extend") then list.extend is 
slightly faster.  (Not surprising, as the function list_inplace_concat 
(+=) calls the function listextend (list.extend) in listobject.c)

(3) That being said, extend_ext is almost certainly premature 
optimization. =)

Steve

[1] You can still use timeit without Python 2.4, but you'll have to call 
timeit.py directly instead of the "python -m timeit" command I used.