Python 1.6 The balanced language

Suchandra Thapa ssthapa at harper.uchicago.edu
Sat Sep 2 21:18:00 CEST 2000


Tim Roberts <timr at probo.com> wrote:
>ssthapa at harper.uchicago.edu (Suchandra Thapa) wrote:
>>With python's lack of referential
>>transparency, this will become a nightmare.  E.g.
>>    def swap(x, y):
>>	t = y[x - 1]
>>	y[x - 1] = x
>>	x = t
>>	print x','y[x-1]
>>
>>    x = 3
>>    y = [3, 2, 1]
>>    swap(x, y)
>>
>>prints 3 , 3 which is probably not the programmer intended.
>
>When I type this into Python 1.5.2, I get 1 , 3.  This is what I expected.
>The outer value of x is not altered, although y is.  Is that what you're
>referring to?
>
> >>> swap(x,y)
> 1 , 3
> >>> x,y
> (3, [3, 2, 3])

    The example I gave would be what types of problems that would  happen 
if python had lazy evaluations.  Currently python has eager evaluations so
the code works correctly.  The discussion was in the context of extensions to
python.



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