i had to implement this today, this is what the class looks like

class Foo(object):
def __init__(self, val):
    self.Value = val
def __eq__(self, other):
    return self.Value == other.Value

foos = [Foo(1), Foo(2)]

xfoo = Foo(2)

print xfoo in foos  # this calls the __eq__ function, will return True

xfoo = Foo(4)

print xfoo in foos  # will return False

when we implement eq [equal], we should also implement ne [not equal] for != or not in operators.