gistfile1.py

class X(object):
def __init__(self, value):
       self.value = value
   def __cmp__(self, other):
       print 'I am %x, comparing my %d with other %x %d' % (id(self), self.value, id(other), other.value)
       return cmp(self.value, other.value)
   
a = [X(2), X(1), X(3)]
X(1) in a