Python 2.x gotchas and landmines

Question

The purpose of my question is to strengthen my knowledge base with Python and get a better picture of it, which includes knowing its faults and surprises. To keep things sp

Answer 1

x += [...] is not the same as x = x + [...] when x is a list`

>>> x = y = [1,2,3]
>>> x = x + [4]
>>> x == y
False

>>> x = y = [1,2,3]
>>> x += [4]
>>> x == y
True

One creates a new list while the other modifies in place