Passing by value instead of reference

[Michael Hudson]

"Jeff Massung" <jmassung at magpiesystems.com> writes:

> Michael Hudson wrote in message ...
> >It will.  I don't think you understand assigment yet...
> >
> 
> 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 ;)

In general, something like:

def test(x):
    import copy
    x=copy.copy(x)
    # or x=copy.deepcopy() (to taste)
    x.append( ... )

just for lists:

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

The latter is fairly idiomatic; I've never used the former (I don't
think).

Cheers,
M.

-- 
112. Computer Science is embarrassed by the computer.
     -- Alan Perlis, http://www.cs.yale.edu/~perlis-alan/quotes.html