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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 Callable, Generic, TypeVar |
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T = TypeVar('T') |
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__all__ = ['ProxySubject', 'Proxy'] |
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class ProxySubjectInterfaceClass(type, Generic[T]): |
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"""Interfacing enabling classes to construct classes (instead of instances). |
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Dynamically creates classes that represent a ProxySubjectInterface. |
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The created classes automatically gain an abstract method with name given at |
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creation time. The input name can match the desired named selected to a |
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proxied object. |
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For example in a scenario where you proxy a remote web server you might |
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create ProxySubjectInterface with a 'make_request' abstract method where as |
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in a scenario where the proxied object is a Tensorflow function you might |
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name the abstract method as 'tensorflow'. |
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Dynamically, creating a class (as this class allows) is useful to adjust to |
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scenarios like the above. |
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Args: |
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Generic ([type]): [description] |
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Raises: |
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NotImplementedError: [description] |
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Returns: |
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[type]: [description] |
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""" |
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def __new__(mcs, *args, **kwargs): |
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def __init__(self, proxied_object): |
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self._proxy_subject = proxied_object |
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def object(self, *args, **kwargs) -> T: |
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return self._proxy_subject |
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return super().__new__( |
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mcs, |
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'ProxySubjectInterface', |
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(ABC,), |
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{ |
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'__init__': __init__, |
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args[0]: object, |
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}, |
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) |
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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
