2017/2/6

描述

比如, 考虑这样一段代码, 它的执行流程是怎样的呢 ?

class Foo(object):

@cached_property

def foo(self):

# calculate something important here

return 42

f = Foo()

f.foo

f.foo

相关代码

以class为基础的缓存装饰器

class cached_property(property):

"""A decorator that converts a function into a lazy property.  The

function wrapped is called the first time to retrieve the result

and then that calculated result is used the next time you access

the value::

class Foo(object):

@cached_property

def foo(self):

# calculate something important here

return 42

The class has to have a `__dict__` in order for this property to

work.

"""

# implementation detail: A subclass of python's builtin property

# decorator, we override __get__ to check for a cached value. If one

# choses to invoke __get__ by hand the property will still work as

# expected because the lookup logic is replicated in __get__ for

# manual invocation.

def __init__(self, func, name=None, doc=None):

self.__name__ = name or func.__name__

self.__module__ = func.__module__

self.__doc__ = doc or func.__doc__

self.func = func

def __set__(self, obj, value):

obj.__dict__[self.__name__] = value

def __get__(self, obj, type=None):

if obj is None:

return self

value = obj.__dict__.get(self.__name__, _missing)

if value is _missing:

value = self.func(obj)

obj.__dict__[self.__name__] = value

return value

上下文环境

产品版本: Python2

操作系统: Linux

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相似的问题: http://stackoverflow.com/ques…

def cached_property(func):

def _deco(*args, **kwargs):

print(22222222222222)

ret = func(*args, **kwargs) #这是调用foo方法

print(44444444444444)

return ret

return _deco

class Foo(object):

def __init__(self):

print (111111111111111111)

@cached_property

def foo(self):

print(3333333333333)

return 42

f = Foo()

f.foo()