# nxpy_memo -------------------------------------------------------------------
# Copyright Nicola Musatti 2008 - 2018
# Use, modification, and distribution are subject to the Boost Software
# License, Version 1.0. (See accompanying file LICENSE.txt or copy at
# http://www.boost.org/LICENSE_1_0.txt)
# See https://github.com/nmusatti/nxpy/tree/master/libs/memo. -----------------
r"""
Memoize class instances according to a given key.
By default the key only assumes the *True* value, thus implementing a singleton.
"""
from __future__ import absolute_import
import nxpy.core.abstract
import nxpy.core.past
if nxpy.core.past.V_2_6.at_least():
import abc
import six
[docs]class Memo(object):
r"""
Base class for classes that require memoization.
Subclasses should override the *_key(\*args, \*\*kwargs)* method to compute a key on the
constructor's arguments.
Care should be taken to avoid calling *__init__()* again for entities already constructed.
"""
#if nxpy.core.past.V_2_6.at_least():
# __metaclass__ = abc.ABCMeta
_dict = {}
[docs] def __new__(cls, *args, **kwargs):
r"""
Return the instance corresponding to the given key, creating it if it doesn't exist.
"""
k = cls._key(*args, **kwargs)
try:
return Memo._dict[(cls, k)]
except KeyError:
i = super(Memo, cls).__new__(cls)
Memo._dict[(cls, k)] = i
return i
if nxpy.core.past.V_2_6.at_least():
@nxpy.core.abstract.abstractstatic
def _key(*args, **kwargs):
r"""
Returns the key by which instances are memoized.
Subclasses should override it as a function of their construction arguments.
"""
return True
else:
@staticmethod
def _key(*args, **kwargs):
return True
if nxpy.core.past.V_2_6.at_least():
Memo = six.add_metaclass(abc.ABCMeta)(Memo)