Interfaces

Adds interfaces to Python. Loosely based on either Java interfaces, or Haskell typeclasses. This provides some informal assurances to client code that your class or objects behave in a certain fashion.

To create an interface, subclass Interface, and add fill out the __name__ and __interface__ fields. Also, adding comments is very necessary, as the details of the interface are left unspecified.

• __name__ is a pretty name for your interface
• __interface__ is a list of attributes that implementors are required to support.

import interfaces

class Strable(Interface):
  '''Anything that can be converted to a (pretty) string.
  To implement, define a function __str__ like so:
  def __str__(self):
    return "Pretty description of " + self.name
  '''
  __name__ = 'Strable'
  __interface__ = [ 
      '__str__',    # obj.__str__(self) returns a pretty string
    ]

Then, to declare that a class is Strable, we use the @implements decorator:

@implements(Strable)
class MyClass:
  def __init__(self, name="Fred"):
    self.name = name

  def __str__(self):
    return "A " + self.name

Of course, the raison d'etre of interfaces is so that you can test for them:

if implements(myobj, Strable):
  print "Foo with your " + str(myobj)