question on list comprehensions

[Alex Martelli]

Mustafa Demirhan <mustafademirhan at gmail.com> wrote:

> Why not just use while loops instead of for loops? You dont have to
> create a new array each time you want a loop - you can simply use an
> index integer.
> 
>     i = 0
>     while i < 5000000:
>         res [0] = res [0] + i
>         i = i + 1
> 
> Takes less than 2 seconds on my laptop.

Sure, this is fine, but low-level twiddling with indices isn't all that
nice.  A compact alternative such as

    res[0] = sum(xrange(5000000))

is, IMHO, preferable to your while loop, not so much because it may be
faster, but because it expresses a single design idea ("let's sum the
first 5 million nonnegative integers") very directly, rather than
getting into the low-level implementation details of _how_ we generate
those integers one after the other, and how we sum them up ditto.


Alex