"""Implementation of the object pool"""
import types
import attr
__all__ = ['ObjectsPool']
def _validate_build_hash_callback(self, attribute, build_hash_callback):
def method(_self, *args, **kwargs):
return build_hash_callback(*args, **kwargs)
setattr(self, attribute.name, types.MethodType(method, self))
[docs]@attr.s
class ObjectsPool:
"""Class of objects that are able to return a reference to an object upon request.
Whenever an object is requested, it is checked whether it exists in the pool.
Then if it exists, a reference is returned, otherwise a new object is
constructed (given the provided callable) and its reference is returned.
Arguments:
constructor (callable): able to construct the object given arguments
objects (dict): the data structure representing the object pool
"""
@staticmethod
def __build_hash(*args, **kwargs):
r"""Construct a hash out of the input \*args and \*\*kwargs."""
return hash('-'.join([str(_) for _ in args] + [f'{key}={str(value)}' for key, value in kwargs.items()]))
constructor = attr.ib()
_build_hash = attr.ib(validator=_validate_build_hash_callback)
_objects = attr.ib(default={})
[docs] def get_object(self, *args, **kwargs):
r"""Request an object from the pool.
Get or create an object given the input parameters. Existence in the pool is done using the
python-build-in hash function. The input \*args and \*\*kwargs serve as
input in the hash function to create unique keys with which to "query" the object pool.
Returns:
object: the reference to the object that corresponds to the input
arguments, regardless of whether it was found in the pool or not
"""
key = self._build_hash(*args, **kwargs)
if key not in self._objects:
self._objects[key] = self.constructor(*args, **kwargs)
return self._objects[key]
[docs] @classmethod
def new_empty(cls, constructor, build_hash=None):
if build_hash is None:
build_hash = ObjectsPool.__build_hash
return ObjectsPool(constructor, build_hash)