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copied!<p>Zope interfaces can provide a useful way to decouple two pieces of code that shouldn't depend on each other.</p> <p>Say we have a component that knows how to print a greeting in module a.py:</p> <pre><code>>>> class Greeter(object): ... def greet(self): ... print 'Hello' </code></pre> <p>And some code that needs to print a greeting in module b.py:</p> <pre><code>>>> Greeter().greet() 'Hello' </code></pre> <p>This arrangement makes it hard to swap out the code that handles the greeting without touching b.py (which might be distributed in a separate package). Instead, we could introduce a third module c.py which defines an IGreeter interface:</p> <pre><code>>>> from zope.interface import Interface >>> class IGreeter(Interface): ... def greet(): ... """ Gives a greeting. """ </code></pre> <p>Now we can use this to decouple a.py and b.py. Instead of instantiating a Greeter class, b.py will now ask for a utility providing the IGreeter interface. And a.py will declare that the Greeter class implements that interface:</p> <pre><code>(a.py) >>> from zope.interface import implementer >>> from zope.component import provideUtility >>> from c import IGreeter >>> @implementer(IGreeter) ... class Greeter(object): ... def greet(self): ... print 'Hello' >>> provideUtility(Greeter(), IGreeter) (b.py) >>> from zope.component import getUtility >>> from c import IGreeter >>> greeter = getUtility(IGreeter) >>> greeter.greet() 'Hello' </code></pre>

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