help with something that ought to be simple

[Matthew Nobes]

Hello all,

I am trying to do something that ought to be very simple, yet for
some reason isn't.

What I want to do it the following.  Take a list of lists, in the
following form

[[0,0,0,0],[1,0,0,0],...,]

and preform some operations on it.

So I wrote a litte script to do this, here's the first bit

def del_2(rho,input,output):

    output=[[0,0,0,0]]

    for i in input:
        i[rho-1]=1
        output.append(i)

so far so good.  This takes the input and appends it, slightly
modified to the output.

Now here comes the problem.  I want to add some more stuff to the
output.  Here's what I try to do:

    temp=[]
    for i in output[2:]:
        temp.append(i)

    for i in temp:
        i[rho-1]=i[rho-1]-1

    for i temp:
        output.append(i)

    return output

I define temp precisly so that I don't mess with output.  What I
want to do is do some stuff to temp, then append that onto the
output from before.  BUT*** everything I do to temp also get's
done to output.  This ends up makeing the earlier stuff get
mucked up

a concrete example:

I input rho=2 and input=[[0,0,0,0],[1,0,0,0]]

after the first step output is

[[0,0,0,0],[0,1,0,0],[1,1,0,0]]

This is what I want.  Now I call that temp, and take the last
entry and make it [1,0,0,0].

Now I did this to temp.  So I should be able to now append this
to output and my result *SHOULD* be
[[0,0,0,0],[0,1,0,0],[1,1,0,0],[1,0,0,0]]

but instead the operation on temp also gets preformed on output
and I get
[[0,0,0,0],[0,1,0,0],[1,0,0,0],[1,0,0,0]]

So my question is how do I stop this from happening?  I must be
something extremely simple, so sorry in advance for asking
something silly...

-- 
``We may feel that at last, unlike all previous generations, we
have found certitude.  They thought so too'' -Robert Conquest
Matthew Nobes, c/o Physics Dept. Simon Fraser University, 8888 University
Drive Burnaby, B.C., Canada, http://www.sfu.ca/~manobes