More flexible type conversion.

[leorochael]

Suppose I have a subclass of list or another class with the same "interface" (say, PersistentList from ZODB). There doesn't seem to be simple way to have a SequenceSchema deserialize to it.

First I have to create a colander.Sequence subclass, override the _impl method, call super, then convert the result to PersistentList before returning it. Then I have to set this colander.Sequence subclass as the schema_type attribute of a SequenceSchema subclass.

It would be nice to have a concrete_class (or concrete_factory) attribute/parameter that could be passed to SchemaNode, which would then be passed to the schema_type constructor which would use it as the constructor of the desserialized appstruct.

[sighalt]

+1 though it seems we are the only two people wishing this feature :(