How to efficiently proceed addition and subtraction in python list?

[Steve Holden]

Ant wrote:
> Tim Chase wrote:
> 
>>>I have a list AAA = [1, 2, 3] and would like to subtract one from list
>>>AAA
>>>so AAA' = [0, 1, 2]
>>>
>>>What should I do?
>>
>>
>>Sounds like a list comprehension to me:
> 
> 
> Also the built in function 'map' would work:
> 
> 
>>>>a = [1,2,3]
>>>>b = map(lambda x: x-1, a)
>>>>b
> 
> [0, 1, 2]
> 
> List comprehensions are more pythonic, but map would probably be faster
> if performance was a (real) issue.
> 
And statements like that are probably going to annoy me ;-)

  >>> t = timeit.Timer("b = map(lambda x: x-1, a)", setup="a=[1,2,3]")
  >>> t.timeit()
2.4686168214116599
  >>> t = timeit.Timer("b = [x-1 for x in a]", setup="a=[1,2,3]")
  >>> t.timeit()
0.9930245324475635
  >>>

Any timing prediction involving the word "probably" isn't worth the 
paper it's written on (or even less if it's posted in a newsgroup ;-). 
If it's "probably" faster, and if performance is *really* important, you 
need to benchmark both options to remove the "probably". As the above 
test makes clear, your assertions are certainly untrue for 2.4.2 on Windows.

regards
  Steve
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