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"""Proxy structural software pattern. |
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This module contains boiler-plate code to supply the Proxy structural software |
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design pattern, to the client code.""" |
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from abc import ABC, abstractmethod |
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from typing import TypeVar, Generic, Callable |
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T = TypeVar('T') |
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__all__ = ['ProxySubject', 'Proxy'] |
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class ProxySubjectInterface(ABC, Generic[T]): |
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"""Proxy Subject interface holding the important 'request' operation. |
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Declares common operations for both ProxySubject and |
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the Proxy. As long as the client uses ProxySubject's interface, a proxy can |
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be passed pass to it, instead of a real subject. |
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""" |
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@abstractmethod |
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def request(self, *args, **kwargs) -> T: |
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raise NotImplementedError |
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class ProxySubject(ProxySubjectInterface, Generic[T]): |
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""" |
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The ProxySubject contains some core business logic. Usually, ProxySubject are |
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capable of doing some useful work which may also be very slow or sensitive - |
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e.g. correcting input data. A Proxy can solve these issues without any |
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changes to the ProxySubject's code. |
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Example: |
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>>> from software_patterns import ProxySubject |
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>>> proxied_operation = lambda x: x + 1 |
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>>> proxied_operation(1) |
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2 |
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>>> proxied_object = ProxySubject(proxied_operation) |
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>>> proxied_object.request(1) |
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2 |
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""" |
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def __init__(self, callback: Callable[..., T]): |
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self._callback = callback |
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def request(self, *args, **kwargs) -> T: |
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return self._callback(*args, **kwargs) |
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class Proxy(ProxySubjectInterface, Generic[T]): |
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""" |
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The Proxy has an interface identical to the ProxySubject. |
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Example: |
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>>> from software_patterns import Proxy |
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>>> from software_patterns import ProxySubject |
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>>> class ClientProxy(Proxy): |
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... def request(self, *args, **kwargs): |
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... args = [args[0] + 1] |
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... result = super().request(*args, **kwargs) |
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... result += 1 |
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... return result |
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>>> proxied_operation = lambda x: x * 2 |
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>>> proxy_subject = ProxySubject(proxied_operation) |
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>>> proxy_subject.request(3) |
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6 |
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>>> proxy = ClientProxy(proxy_subject) |
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>>> proxy.request(3) |
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9 |
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""" |
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def __init__(self, proxy_subject: ProxySubject): |
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self._proxy_subject = proxy_subject |
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def request(self, *args, **kwargs) -> T: |
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""" |
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The most common applications of the Proxy pattern are lazy loading, |
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caching, controlling the access, logging, etc. A Proxy can perform one |
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of these things and then, depending on the result, pass the execution to |
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the same method in a linked ProxySubject object. |
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""" |
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return self._proxy_subject.request(*args, **kwargs) |
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boromir674 /
software-patterns
