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# -*- coding: utf-8 -*-
# decorators.py
# Copyright (C) 2013 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
Useful decorators.
"""
import collections
import datetime
import functools
import logging
logger = logging.getLogger(__name__)
class _memoized(object):
"""
Decorator.
Caches a function's return value each time it is called.
If called later with the same arguments, the cached value is returned
(not reevaluated).
"""
# cache invalidation time, in seconds
CACHE_INVALIDATION_DELTA = 1800
def __init__(self, func, ignore_kwargs=None, is_method=False,
invalidation=None):
"""
:param ignore_kwargs: If True, ignore all kwargs.
If tuple, ignore those kwargs.
:type ignore_kwargs: bool, tuple or None
:param is_method: whether the decorated function is a method.
(ignores the self argument if so).
:type is_method: True
"""
self.ignore_kwargs = ignore_kwargs if ignore_kwargs else []
self.is_method = is_method
self.func = func
if invalidation:
self.CACHE_INVALIDATION_DELTA = invalidation
# TODO should put bounds to the cache dict so we do not
# consume a huge amount of memory.
self.cache = {}
self.cache_ts = {}
def __call__(self, *args, **kwargs):
"""
Executes the call.
:tyoe args: tuple
:type kwargs: dict
"""
def ret_or_raise(value):
"""
Returns the value except if it is an exception,
in which case it's raised.
"""
if isinstance(value, Exception):
raise value
return value
if self.is_method:
# forget about `self` as key
key_args = args[1:]
else:
key_args = args
if self.ignore_kwargs is True:
key = key_args
else:
key = (key_args, frozenset(
[(k, v) for k, v in kwargs.items()
if k not in self.ignore_kwargs]))
if not isinstance(key, collections.Hashable):
# uncacheable. a list, for instance.
# better to not cache than blow up.
logger.warning("Key is not hashable, bailing out!")
return self.func(*args, **kwargs)
if key in self.cache:
if self._is_cache_still_valid(key):
value = self.cache[key]
logger.debug("Got value from cache...")
return ret_or_raise(value)
else:
logger.debug("Cache is invalid, evaluating again...")
# no cache, or cache invalid
try:
value = self.func(*args, **kwargs)
except Exception as exc:
logger.error("Exception while calling function: %r" % (exc,))
value = exc
self.cache[key] = value
self.cache_ts[key] = datetime.datetime.now()
return ret_or_raise(value)
def _is_cache_still_valid(self, key, now=datetime.datetime.now):
"""
Returns True if the cache value is still valid, False otherwise.
For now, this happen if less than CACHE_INVALIDATION_DELTA seconds
have passed from the time in which we recorded the cached value.
:param key: the key to lookup in the cache
:type key: hashable
:param now: a callable that returns a datetime object. override
for dependency injection during testing.
:type now: callable
:rtype: bool
"""
cached_ts = self.cache_ts[key]
delta = datetime.timedelta(seconds=self.CACHE_INVALIDATION_DELTA)
return (now() - cached_ts) < delta
def __repr__(self):
"""
Return the function's docstring.
"""
return self.func.__doc__
def __get__(self, obj, objtype):
"""
Support instance methods.
"""
return functools.partial(self.__call__, obj)
def memoized_method(function=None, ignore_kwargs=None):
"""
Wrap _memoized to allow for deferred calling
:type function: callable, or None.
:type ignore_kwargs: None, True or tuple.
"""
if function:
return _memoized(function, is_method=True)
else:
def wrapper(function):
return _memoized(
function, ignore_kwargs=ignore_kwargs, is_method=True)
return wrapper
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