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"""Implementation of the Memoize Software Design Pattern. |
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Memoize is implemented using an Object Pool which is queried by a key which is |
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the result of computing a hash given runtime arguments. |
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""" |
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import types |
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from typing import Any, Callable, Dict, Generic, Optional, TypeVar, Union |
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__all__ = ['ObjectsPool'] |
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DictKey = Union[int, str] |
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ObjectType = TypeVar('ObjectType') |
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RuntimeBuildHashCallable = Callable[..., Union[int, str]] |
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def adapt_build_hash(a_callable: RuntimeBuildHashCallable): |
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def build_hash(_self: ObjectType, *args, **kwargs): |
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return a_callable(*args, **kwargs) |
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return build_hash |
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class ObjectsPool(Generic[ObjectType]): |
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"""Cache objects and allow to query (the pool) using runtime arguments. |
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Instances of the ObjectsPool class implement the Object Pool Software Design |
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Creational Pattern. |
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Whenever an object is requested, it is checked whether it exists in the |
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pool by using the runtimetime arguments to query a python dictionary. |
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If it exists, a reference is returned, otherwise a new object is |
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constructed (given the provided callback) and its reference is returned. |
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Example: |
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>>> from software_patterns import ObjectsPool |
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>>> class ClientClass: |
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... def __init__(self, a: int, b: int): |
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... pass |
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>>> object_pool = ObjectsPool[ClientClass](ClientClass) |
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>>> obj1 = object_pool.get_object(1, 2) |
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>>> obj2 = object_pool.get_object(1, 3) |
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>>> obj3 = object_pool.get_object(1, 2) |
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>>> id(obj1) == id(obj3) |
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True |
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>>> len(object_pool._objects) |
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2 |
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Args: |
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callback (Callable[..., ObjectType]): constructs objects given arguments |
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hash_callback (Optional[RuntimeBuildHashCallable], optional): option to |
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overide the default hash key computer. Defaults to None. |
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Returns: |
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[type]: [description] |
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""" |
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_objects: Dict[DictKey, ObjectType] |
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user_supplied_callback: Dict[bool, Callable] = { |
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True: lambda callback: callback, |
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False: lambda callback: ObjectsPool.__build_hash, |
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} |
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def __init__( |
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self, |
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callback: Callable[..., ObjectType], |
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hash_callback: Optional[RuntimeBuildHashCallable] = None, |
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): |
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self.constructor = callback |
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build_hash_callback = self.user_supplied_callback[callable(hash_callback)]( |
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hash_callback |
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) |
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self._build_hash = types.MethodType(adapt_build_hash(build_hash_callback), self) |
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self._objects = {} |
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@staticmethod |
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def __build_hash(*args: Any, **kwargs: Any) -> int: |
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r"""Construct a hash out of the input \*args and \*\*kwargs.""" |
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return hash( |
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'-'.join( |
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[str(_) for _ in args] |
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+ [f'{key}={str(value)}' for key, value in kwargs.items()] |
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) |
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) |
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def get_object(self, *args: Any, **kwargs: Any) -> ObjectType: |
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r"""Request an object from the pool. |
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Get or create an object given the input arguments, which are used to |
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create a unique hash key. The key is used to query a python dictionary |
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and determine whether the object request refers to a cached object. |
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Returns: |
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object (ObjectType): the reference to the object that corresponds to the input |
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arguments, regardless of whether it was found in the pool or not |
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""" |
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key = self._build_hash(*args, **kwargs) |
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if key not in self._objects: |
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self._objects[key] = self.constructor(*args, **kwargs) |
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return self._objects[key] |
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boromir674 /
software-patterns
