Question

Is it possible to implement a method of a class so that objects of it works with set() function? So Set(objarray) would return unique objects. Of course, creating my own set is an option, but I just don’t want to reinvent the wheel if it is already there.

EDIT : I think I got your guys confused with my English. This is what I have in my class – I have a Person class that has person name and address as its members. This is what I want to do –

persons = []
for i in range (50):
  name = raw_input("Enter Name")
  address = raw_input("Address")
  persons.append(Person(name,address))
unique = Set(persons) #would only return one person from an address. 
                      #The rest from the same address will be removed

I hope that clear confusion.

Answer 1

Yes. First, if your class implements neither __hash__ nor __eq__, then they are already hashable (the id is used as the hash value and comparisons are done by is).

Or, if you implement __hash__ and __eq__, then your class instances can be safely used in a set or as dictionary keys:

>>> class Foo:
...     def __init__(self, val): self.val = val
...     def __hash__(self): return hash(self.val)
...     def __eq__(self, other): return self.val == other.val
...     def __repr__(self): return 'Foo(%r)' % self.val
... 
>>> print set([Foo(3), Foo("bar")])
set([Foo(3), Foo('bar')])

If you want to be able to call set directly on instances of your class, overload __iter__ so that the class instances appear to be iterable:

>>> class CharSeq:
...     def __init__(self, first, last):
...         self.first = ord(first)
...         self.last = ord(last)
...     def __iter__(self):
...         return (chr(i) for i in xrange(self.first, self.last+1))
... 
>>> set(CharSeq('a', 'c'))
set(['a', 'c', 'b'])