 | __eq__(self, x): for equality (a==b), should return True or False |
| __cmp__(self, x): for comparison (<, <=, >, >=, ==, !=); return negative integer, zero or positive integer if self is less than, equal or greater than x (resp.) |
| __len__(self): length of object (called by len(x)) |
| __call__(self [, args]): calls like a(x,y) implies a.__call__(x,y) |
