PyProtocols extends the PEP 246 adapt() function with a new "declaration
API" that lets you easily define your own protocols and adapters, and
declare what adapters should be used to adapt what types, objects, or
protocols.  In addition to its own Interface type, PyProtocols can also use
Twisted and Zope's Interface types too.  (Of course, since Twisted and Zope
interfaces aren't as flexible, only a subset of the PyProtocols API works
with them.  Specific limitations are listed in the documentation.)

If you're familiar with Interface objects in Zope, Twisted, or PEAK, the
Interface objects in PyProtocols are very similar. But, they can also do
many things that no other Python interface types can do. For example,
PyProtocols supports "subsetting" of interfaces, where you can declare that
one interface is a subset of another existing interface. This is like
declaring that somebody else's existing interface is actually a subclass of
the new interface. Twisted and Zope don't allow this, which makes them very
hard to use if you're trying to define interfaces like "Read-only Mapping"
as a subset of "Mapping Object".