[Tutor] Efficiency

[naheed arafat]

On Sat, Jun 25, 2011 at 9:42 PM, Steven D'Aprano <steve at pearwood.info>wrote:

> naheed arafat wrote:
>
>> 1)
>>
>>> zip('How are you?'.split(' ')[::-1],'i am fine.'.split(' '))
>>>>>
>>>> [('you?', 'i'), ('are', 'am'), ('How', 'fine.')]
>>
>>> map(lambda i,j:(i,j),'How are you?'.split(' ')[::-1],'i am
>>>>>
>>>> fine.'.split(' '))
>> [('you?', 'i'), ('are', 'am'), ('How', 'fine.')]
>>
>> Which one has better efficiency?
>>
>
> Define "efficiency".
>
> Do you mean:
>
> - most efficient for the programmer to write?
> - easiest to read?
> - fastest for the compiler to compile?
> - uses the smallest number of characters in source code?
> - takes up the least space on disk when compiled?
> - runs fastest?
> - uses least memory?
> - easiest to maintain when you need to make changes?
> - easiest to debug when you discover a bug?
>
> I meant "runs fastest" .

Before trying to optimize your code, you should consider whether you are
> wasting your time or not. Chances are good that you are. You should consider
> these famous quotes about optimization:
>
>
> "More computing sins are committed in the name of efficiency (without
> necessarily achieving it) than for any other single reason - including blind
> stupidity." - W.A. Wulf
>
>
I don't know what is meant by computing sins.. would you please clarify in
which cases optimization would be a waste of time?


> "We should forget about small efficiencies, say about 97% of the time:
> premature optimization is the root of all evil. Yet we should not pass up
> our opportunities in that critical 3%. A good programmer will not be lulled
> into complacency by such reasoning, he will be wise to look carefully at the
> critical code; but only after that code has been identified." - Donald Knuth
>
>

> "Bottlenecks occur in surprising places, so don't try to second guess and
> put in a speed hack until you have proven that's where the bottleneck is." -
> Rob Pike
>
>
what is meant by Bottleneck?


> "The First Rule of Program Optimization: Don't do it. The Second Rule of
> Program Optimization (for experts only!): Don't do it yet." - Michael A.
> Jackson
>


> I believe that the only efficiency you should care about initially is the
> efficiency of *reading* (and to a lesser extent, writing) good, readable,
> easily maintained code. So long as you avoid common-sense mistakes, who
> cares if you can speed up your script from 2.5 milliseconds to 1.5 ms? Who
> is going to notice?
>
> (On the other hand, if your script really is too slow, that's a different
> story!)
>
>
>
>
>  2)
>> Is there any way easier to do the following?
>> input:
>> 'How are you'
>> 'I am fine'
>> output:
>> 'you I are am How fine'
>>
>> solution:
>>
>>> ' '.join(reduce(lambda x,y:x+y, zip('How are you'.split(' ')[::-1],
>>>>>
>>>> 'I am fine'.split(' '))))
>>
>
> That will work well for small amounts of data, say, a few hundred words or
> so. But for large amounts of data, it will be slow and inefficient. It's
> best to avoid such one-liners when possible, they tend to be slow.
>
>  I was learning the use of lambda. And as assignment (may be) doesn't work
inside lambda's i tried such one-liners..but didn't know such one-liners are
slow for huge data..thank you for your suggestion.

I would solve it like this:
>
> import itertools
> a = reversed('How are you'.split(' '))
> b = 'I am fine'.split(' ')
> words = itertools.chain(*zip(a, b))
> ' '.join(words)
>
>
>
> --
> Steven
>
>
>  zip() takes sequences as argument.Isn't variable a an iterable object? the
code didn't work.

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