与cached_property捕获异常
问题描述:
我试图赶上使用decorator
异常的cached_property
https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76与cached_property捕获异常
https://pypi.python.org/pypi/cached-property
我愿做如下简单的东西,但是这并不工作
from pprint import pprint
import time
from cached_property import cached_property
class MyException(Exception):
pass
def catch_my_exceptions(fn):
def wrapped(*args, **kwargs):
try:
return fn(*args, **kwargs)
except MyException as e:
cls = args[0]
err = 'Found error at {}: {}'.format(time.asctime(), e)
cls.error_msgs.append(err)
print(err)
return
return wrapped
class Foo(object):
def __init__(self):
self.vars = {}
@cached_property
@catch_my_exceptions
def is_cache_working(self):
self.vars[time.asctime()] = True
time.sleep(3)
print('running cache runner')
return time.asctime()
fo = Foo()
for i in range(3):
print(fo.is_cache_working)
pprint(fo.vars)
# This doesn't trigger caching
running cache runner
Thu Feb 23 21:45:15 2017
{'Thu Feb 23 21:45:11 2017': True}
running cache runner
Thu Feb 23 21:45:18 2017
{'Thu Feb 23 21:45:11 2017': True, 'Thu Feb 23 21:45:15 2017': True}
running cache runner
Thu Feb 23 21:45:21 2017
{'Thu Feb 23 21:45:11 2017': True,
'Thu Feb 23 21:45:15 2017': True,
'Thu Feb 23 21:45:18 2017': True}
# Current solution that works:
我的这一切是做以下事情。有人可以建议我一个更好的方法。还我怎么会传例外列表这个my_cached_decorator
import time
from pprint import pprint
from cached_property import cached_property
class MyException(Exception):
pass
class my_cached_property(cached_property):
def __init__(self, func):
super(self.__class__, self).__init__(func)
def __get__(self, obj, cls):
try:
super(self.__class__, self).__get__(obj, cls)
except MyException as e:
err = 'Found error at {}: {}'.format(time.asctime(), e)
print(err)
value = obj.__dict__[self.func.__name__] = None
return value
class Foo(object):
def __init__(self):
self.vars = {}
@my_cached_property
def is_cache_working(self):
self.vars[time.asctime()] = True
time.sleep(3)
print('running cache runner')
raise MyException('fooobar')
return time.asctime()
fo = Foo()
for i in range(3):
print(fo.is_cache_working)
pprint(fo.vars)
答
它可能不是最好的解决办法,但你将有机会获得内部功能从装饰到主叫方返回,还从装饰的闭包内。
例子:
def decorator(f):
def wrapper(*args, **kwargs):
try:
f(*args, **kwargs)
except Exception as e:
wrapper.__dict__.setdefault('errors', []).append(e)
return wrapper
@decorator
def raiser():
raise Exception('Oh no!')
> raiser()
> raiser.errors
[Exception('Oh no!')]
答
好吧,我想通了这个问题,它是在方式cached_property作品。为了缓存它,它会将该值写入实例,并使用与其封装的函数相同的名称。问题在于它包装的函数的名称的名称为“包装”,来自装饰器。所以,如果你在初始的fo.is_cache_working之后访问过fo.wrapped,你会得到你的缓存结果。
没有简单的方法将两个想法混合在一起。最简单的解决方案是编写自己的cached_property,它自己存储该值:
class cached_property(object):
def __init__(self, func):
self.func = func
# you can store other function attributes here - such as __doc__ - if you want
self.values = {}
def __get__(self, instance, owner):
if instance in self.values:
return self.values[instance]
else:
value = self.values[instance] = self.func(instance)
return value