On Nov 6, 6:12 am, kj <no.em...@[...].post>  wrote:
>  In Perl one can assign a value to any element of an array, even to
>  ones corresponding to indices greater or equal than the length of
>  the array:
> 
>    my @arr;
>    $arr[999] = 42;
> 
>  perl grows the array as needed to accommodate this assignment.  In
>  fact one common optimization in Perl is to "pre-grow" the array to
>  its final size, rather than having perl grow it piecemeal as required
>  by assignments like the one above:
> 
>    my @arr;
>    $#arr = 999_999;
> 
>  After assigning to $#arr (the last index of @arr) as shown above,
>  @arr has length 1,000,000, and all its elements are initialized to
>  undef.
> 
>  In Python the most literal translation of the first code snippet
>  above triggers an IndexError exception:
> 
>  >>> arr = list()
>  >>> arr[999] = 42
> 
>  Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
>  IndexError: list assignment index out of range
> 
>  In fact, one would need to pre-grow the list sufficiently to be
>  able to make an assignment like this one.  I.e. one needs the
>  equivalent of the second Perl snippet above.
> 
>  The best I can come up with is this:
> 
>  arr = [None] * 1000000
> 
>  Is this the most efficient way to achieve this result?
> 
>  TIA!
> 
>  kynn

I don't have the code with me, but for huge arrays, I have used
something like:

> >> arr[0] = initializer
> >> for i in range N:
> >>      arr.extend(arr)

This doubles the array every time through the loop, and you can add
the powers of 2 to get the desired result.
Gil
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