[Tutor] Python oddity

[Tiger12506]

Python lists are mutable. All mutable objects will behave in the fashion you 
described, whereas immutable objects -- tuples, integer, floats, etc. --  
will behave in the fashion that you expect.

This is because python keeps references to objects. When you say bb = aa, 
you are really saying, "Take the reference to the list 'aa' and copy it to 
'bb' so that when you use the variable bb you are just using the a copy of 
the original reference to the *same* object."

Here's another gotcha:

s = [[]]*100  #Thinking that you can initialize a hundred lists easily
s[0].append(1)  #Add something to the first list

And, oh crap, it added a one to all of the lists.