python list handling and Lisp list handling

Arnaud Delobelle arnodel at googlemail.com
Fri Apr 24 20:54:34 CEST 2009


Mark Tarver <dr.mtarver at ukonline.co.uk> writes:
> Ah;  so this
>
> def cons (x,y):
>   return [x] + y
>
> is not accurate?

Depends what you mean by accurate!

in lisp, if you do:

    (setq a '(1 2))
    (setq b (cons 0 a))
    (rplaca a 3)

Then
    a is now (3 2)
    b is now (0 3 2)
    
In Python, if you do:

    a = [1, 2]
    b = cons(0, a) # with your definition of cons
    a[0] = 3

Then
    a is now [3, 2]
    b is now [0, 1, 2]

So in this respect, it is not accurate.  But that's because Python lists
are vectors not conses.

-- 
Arnaud



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