Passing by value instead of reference

[Quinn Dunkan]

On Wed, 10 May 2000 13:33:52 -0600, Jeff Massung <jmassung at magpiesystems.com>
wrote:
>Sorry, I don't ;) - I was thinking like this (I understand how my previous
>example was wrong).
>
>>>> def test(x):
>          x.append(3)
>>>> z = [1,2]
>>>> test(z)
>>>> z
>[1, 2, 3]
>>>>
>
>How can I get x to have the value of z, modify it, and use the modified
>value, without z being modified overall? Thanks, guys ;)

Make a copy:

def test(x):
    x_copy = x[:]
    x_copy.append(3)
    print x_copy

z = [1, 2]
test(z)

Although usually I'd write a function to operate on its args in place, and the
caller can pass a copy if that's what he wants.  Actualy, usually I write a
method which naturally operates on its self in-place :)  Also see the `copy'
module for deep copies.