I was using IDLE (Python GUI) for Python 3.3.3. I don't know if this is a bug or you guys intend it to be this way:

>>> x=[1,2]
>>> y=x
>>> y.append(3)
>>> x
[1, 2, 3]

personally i'd prefer x stays as [1,2] when i'm trying to mutate y

also:
>>> def f1(m,n=['haha']):
	if m==n:
		print('m==n')
	else:
		print('m!=n')
	n.append('yaya')
	
>>> f1(['haha'])
m==n
>>> f1(['haha'])
m!=n

I'd prefer getting consistent results when calling functions like f1