A common mistake. Don't fall into the trap!

Python pointers educational

"""
Educational code snippet for testing pointers familiarity.
Guess the output and find the bad practice.
"""

class Cat:
    def __init__(self, s):
        self.state = s

def observe(cats):
    new_cats = []
    for cat in cats:
        print cat.state, 
    print "\n**"
    for cat in cats:
        print cat.state, 
        new_cats.append(Cat(cat.state))
        cat.state = "dead"
    new_cats = [new_cats[0], new_cats[0]]
    return new_cats

cat1 = Cat("alive")
cats = [cat1, cat1]    
cats = observe(cats)
print "\n--"
for cat in cats:
    print cat.state,