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# Copright 2008 Divmod, Inc. See LICENSE file for details.
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# -*- test-case-name: epsilon.test.test_expose -*-
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This module provides L{Exposer}, a utility for creating decorators that expose
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methods on types for a particular purpose.
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The typical usage of this module is for an infrastructure layer (usually one
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that allows methods to be invoked from the network, directly or indirectly) to
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provide an explicit API for exposing those methods securely.
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For example, a sketch of a finger protocol implementation which could use this
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to expose the results of certain methods as finger results::
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fingermethod = Exposer("This object exposes finger methods.")
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class FingerProtocol(Protocol):
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def __init__(self, fingerModel):
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self.model = fingerModel
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def fingerQuestionReceived(self, whichUser):
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method = fingermethod.get(self.model, whichUser)
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except MethodNotExposed:
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method = lambda : "Unknown user"
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from tx_finger import fingermethod
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class MyFingerModel(object):
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@fingermethod.expose("bob")
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return "Bob is great."
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Assuming lots of protocol code to hook everything together, this would then
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allow you to use MyFingerModel and 'finger bob' to get the message 'Bob is
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from types import FunctionType
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class MethodNotExposed(Exception):
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The requested method was not exposed for the purpose requested. More
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specifically, L{Exposer.get} was used to retrieve a key from an object
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which does not expose that key with that exposer.
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class NameRequired(Exception):
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L{Exposer.expose} was used to decorate a non-function object without having
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a key explicitly specified.
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class Exposer(object):
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This is an object that can expose and retrieve methods on classes.
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@ivar _exposed: a dict mapping exposed keys to exposed function objects.
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def __init__(self, doc):
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def expose(self, key=None):
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Expose the decorated method for this L{Exposer} with the given key. A
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method which is exposed will be able to be retrieved by this
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L{Exposer}'s C{get} method with that key. If no key is provided, the
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key is the method name of the exposed method.
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@someExposer.expose('foo')
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def unrelatedMethodName(): ...
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@param key: a hashable object, used by L{Exposer.get} to look up the
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decorated method later. If None, the key is the exposed method's name.
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@return: a 1-argument callable which records its input as exposed, then
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def decorator(function):
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if isinstance(function, FunctionType):
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rkey = function.__name__
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if rkey not in self._exposed:
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self._exposed[rkey] = []
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self._exposed[rkey].append(function)
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def get(self, obj, key):
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Retrieve 'key' from an instance of a class which previously exposed it.
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@param key: a hashable object, previously passed to L{Exposer.expose}.
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@return: the object which was exposed with the given name on obj's key.
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@raise MethodNotExposed: when the key in question was not exposed with
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if key not in self._exposed:
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raise MethodNotExposed()
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rightFuncs = self._exposed[key]
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for subT in inspect.getmro(T):
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for name, value in subT.__dict__.items():
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for rightFunc in rightFuncs:
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if value is rightFunc:
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raise MethodNotExposed()
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return value.__get__(obj, T)
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raise MethodNotExposed()
added
removed
Epsilon/epsilon/expose.py
