All types in Python are references. That means you cannot re-assign an actual variable and expect it to change the original variable. However, you can certainly modify a variable through a "reference" which is automatically created on copy.
a = [1,2,3]
b = a
b[0] = 0
print a
Output
[0,2,3]
If you want to delete a list via a reference, you can use the other solution or do the following:
b[:] = []