[Python-Dev] performance of {} versus dict()

[Chris Withers]

Hi All,

A colleague pointed me at Doug's excellent article here:

http://www.doughellmann.com/articles/misc/dict-performance/index.html

...which made me a little sad, I suspect I'm not the only one who finds:

a_dict = dict(
     x = 1,
     y = 2,
     z = 3,
     ...
     )

...easier to read than:

a_dict = {
     'x':1,
     'y':2,
     'z':3,
     ...
     }

What can we do to speed up the former case?

Here's comparison for different versions of CPython:

$ python2.5 -m timeit -n 1000000 -r 5 -v 'dict(a=1,b=2,c=3,d=4,e=5,f=6,g=7)'
raw times: 2.96 2.49 2.47 2.42 2.42
1000000 loops, best of 5: 2.42 usec per loop
$ python2.5 -m timeit -n 1000000 -r 5 -v 
"{'a':1,'b':2,'c':3,'d':4,'e':5,'f':6,'g':7}"
raw times: 1.69 1.71 1.68 1.68 1.68
1000000 loops, best of 5: 1.68 usec per loop

$ python2.6 -m timeit -n 1000000 -r 5 -v 'dict(a=1,b=2,c=3,d=4,e=5,f=6,g=7)'
raw times: 2.41 2.41 2.42 2.44 2.41
1000000 loops, best of 5: 2.41 usec per loop
$ python2.6 -m timeit -n 1000000 -r 5 -v 
"{'a':1,'b':2,'c':3,'d':4,'e':5,'f':6,'g':7}"
raw times: 1.51 1.51 1.52 1.51 1.51
1000000 loops, best of 5: 1.51 usec per loop

$ python2.7 -m timeit -n 1000000 -r 5 -v 'dict(a=1,b=2,c=3,d=4,e=5,f=6,g=7)'
raw times: 2.32 2.31 2.31 2.32 2.31
1000000 loops, best of 5: 2.31 usec per loop
$ python2.7 -m timeit -n 1000000 -r 5 -v 
"{'a':1,'b':2,'c':3,'d':4,'e':5,'f':6,'g':7}"
raw times: 1.49 1.49 1.77 1.76 1.55
1000000 loops, best of 5: 1.49 usec per loop

So, not the 6 times headline figure that Doug quotes, but certainly a 
difference. Can someone with Python 3 handy compare there too?

cheers,

Chris

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