How do I stop a Python function from modifying its inputs?
<p>I've asked almost this just before now, but the fix doesn't work for x = [[]], which I'm guessing is because it is a nested list, which is what I will be working with.</p>

<pre><code>def myfunc(w):
 y = w[:]
 y[0].append('What do I need to do to get this to work here?')
 y[0].append('When I search for the manual, I get pointed to python.org, but I can\'t find the answer there.')
 return y

x = [[]]
z = myfunc(x)
print(x)
</code></pre>
