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Inner Method Dispatch for Python

Project Description

Pyta = Python + Beta

Inspired by: http://www.cs.utah.edu/plt/publications/oopsla04-gff.pdf

Usage

Inner dispatch is used to guarantee pre- and post-conditions without using auxiliary methods. An external dispatch results in the lowest method that calls inner being called. An inner(cls, self) call calls the next highest method that has an inner call, or the highest method if there is no higher inner method. super works the same as before, but take care not to cause an infinite loop.

Full example:

from pyta import inner, BetaMetaclass

class A(object):
    def foo(self):
        print "world!"

class B(A): # Can inherit from regular classes
    # The lowest class in the hierarchy that uses `inner` needs the metaclass
    __metaclass__ = BetaMetaclass

    def foo(self):
        inner(B, self).foo() # Calls C.foo
        super(B, self).foo() # Calls A.foo

class C(B):
    def foo(self):
        print "Hello, "

obj = C()
obj.foo() # External dispatch; calls B.foo

Caveats

Because using inner in a superclass completely changes which method an external dispatch resolves to (it’s no longer the most-overriding method) the metaclass is required to inspect the source of the methods and sprinkle some magic to make it all work.

In order for everything to work properly, you must call inner(cls, self) lexically. In other words, it won’t work if you do this:

bar = inner
bar(cls, self).foo()

Or this:

from pyta import inner as bar
bar(cls, self).foo()

Currently, the implementation doesn’t distinguish between strings vs. actual method calls, so if your method contains a string like "text inner( moretext", it’ll break everything.

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0.1.1

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0.1.0

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