dicts extended

[mlenzen]

Dicts could get the same treatment as Collections. The std lib or common libraries support most of these individually, but what if you want a multidict with a default factory? Or a frozen multidict?

• default value
• default_factory function
• multidict
• ordered / indexed?
• frozen
• bijection

[mlenzen]

default_value and default_factory_function could be one single default parameter. Assume it is a callable factory. If calling the obj raises a TypeError: cls is not calllable, then treat default as a default value. The one tricky situation here is if you want to use a callable object as the default value. In this case, you'd have to pass default=lambda: callable.

MultiDict - we could allow the user to select the values collection class. A bag would be the default, but set, ListExtended and setlist along with their frozen variations could all be options to have ordered and/or unique values. We would have to use our ListExtended so that all Collections had the same api for adding/removing elements. Maybe ordered and unique attributes would be inherited/specified by the dict. Extending this idea to the keys gives the interpretation that an indexed dict has a keys setlist.

The keys, values and items views would be instances of the SetList, Bag, Set & List (or ListExtended) abstract base classes.

Class	Key-Value Relationship	Keys Collection	Values Collection
dict	Many-to-One	set	bag
MultiDict	Many-to-Many	bag	bag
bijection	One-to-One	set	set
???	One-to-Many	bag	set

ordering / indexing and freezing are orthogonal to these concerns