Download Traits 4 User Manual

Traits 4 User Manual, Release 4.5.0-rc.1
Implementation details
The algorithm for finding a sequence of adapters adapting an object adaptee to a protocol to_protocol is based
on a weighted graph.
Nodes on the graphs are protocols (types or interfaces).
offer.from_protocol to a offer.to_protocol.
Edges are adaptation offers that connect a
Edges connect protocol A to protocol B and are weighted by two numbers in this priority:
1. a unit weight (1) representing the fact that we use 1 adaptation offer to go from A to B
2. the number of steps up the type hierarchy that we need to take to go from A to offer.from_protocol, so
that more specific adapters are always preferred
The algorithm finds the shortest weighted path between adaptee and to_protocol. Once a candidate path is
found, it tries to create the chain of adapters using the factories in the adaptation offers that compose the path. If this
fails because of conditional adaptation (i.e., an adapter factory returns None), the path is discarded and the algorithm
looks for the next shortest path.
Cycles in adaptation are avoided by only considering path were every adaptation offer is used at most once.
Migration guide
The implementation of the adaptation mechanism changed in Traits 4.4.0 from one based on PyProtocols to a new,
smaller, and more robust implementation.
Code written against traits.protocols will continue to work, although the traits.protocols API has been deprecated and its members will log a warning the first time they are accessed. The traits.protocols package will
be removed in Traits 5.0 .
This is a list of replacements for the old API:
• traits.protocols.api.AdaptationFailure
Use traits.api.AdaptationError instead.
• traits.api.adapts()
Use the traits.api.register_factory() function.
• implements()
Use the traits.api.provides() decorator instead.
• traits.protocols.api.declareAdapter()
Use
the
function
traits.api.register_factory(),
or
the
function
traits.adaptation.api.register_offer() instead. It is no longer necessary to distinguish
between “types”, “protocols”, and “objects”.
• traits.protocols.api.declareImplementation()
This function was used occasionally to declare that an arbitrary type (e.g., dict) implements an interface. Users
that use Python ABCs can use the register method for achieving the same result. Otherwise, use the function
traits.adaptation.api.register_provides() that declares a “null” adapter to adapt the type to
the interface.
• Testing if a class is an Interface
issubclass(klass, Interface) is not reliable, use traits.api.isinterface() instead
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Chapter 1. User Reference