http://code.activestate.com/recipes/tags/mutableset/2009-10-29T21:08:22-07:00ActiveState Code Recipes2009-10-29T21:08:22-07:00Gabriel Genellinahttp://code.activestate.com/recipes/users/924636/http://code.activestate.com/recipes/576932-sets-with-a-custom-equalityuniqueness-function/

<p style="color: grey"> Python recipe 576932 by <a href="/recipes/users/924636/">Gabriel Genellina</a> (<a href="/recipes/tags/abstract_base_class/">abstract_base_class</a>, <a href="/recipes/tags/mutableset/">mutableset</a>, <a href="/recipes/tags/set/">set</a>, <a href="/recipes/tags/unique/">unique</a>). Revision 4. </p> <p>The builtin <code>set</code> and <code>frozenset</code> types are based on object equality; they call __eq__ to determine whether an object is a member of the set or not. But there are cases when one needs a set of objects that are compared by other means, apart from the default __eq__ function. There are several ways to achieve that; this recipe presents two classes, FrozenKeyedSet and KeyedSet, that take an additional function <code>key</code> which is used to determine membership and uniqueness. Given two objects which return the same value for <code>key</code>, only one of them will be in the set.</p>