Le 01/03/2012 19:07, Guido van Rossum a écrit :
What other use cases are there?
frozendict could be used to implement "read-only" types: it is not possible to add or remove an attribute or set an attribute value, but attribute value can be a mutable object. Example of an enum with my type_final.patch (attached to issue #14162).
class Color: ... red=1 ... green=2 ... blue=3 ... __final__=True ... Color.red 1 Color.red=2 TypeError: 'frozendict' object does not support item assignment Color.yellow=4 TypeError: 'frozendict' object does not support item assignment Color.__dict__ frozendict({...})
The implementation avoids the private PyDictProxy for read-only types, type.__dict__ gives directly access to the frozendict (but type.__dict__=newdict is still blocked). The "__final__=True" API is just a proposition, it can be anything else, maybe a metaclass. Using a frozendict for type.__dict__ is not the only possible solution to implement read-only types. There are also Python implementation using properties. Using a frozendict is faster than using properties because getting an attribute is just a fast dictionary lookup, whereas reading a property requires to execute a Python function. The syntax to declare a read-only class is also more classic using the frozendict approach. Victor