___Enter___和___EXIT___在Python装饰器类中如何工作?

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我试图创建一个装饰器类来计算一个函数被调用的次数,但是我收到一条错误消息:

    "TypeError: __exit__() takes exactly 1 argument (4 given)"

我真的不知道我如何给出四个论点。我的代码如下所示:

class fcount2(object):
    __instances = {}
    def __init__(self, f):
        self.__f = f
        self.__numcalls = 0
        fcount2.__instances[f] = self

    def __call__(self, *args, **kwargs):
        self.__numcalls += 1
        return self.__f(*args, **kwargs)

    def __enter__(self):
        return self

    def __exit__(self):
        return self

    @staticmethod
    def count(f):
        return fcount2.__instances[self.__f].__numcalls


@fcount2
def f(n):
    return n+2

for n in range(5):
    print f(n)   
print 'f count =',f.count

def foo(n):
    return n*n

with fcount2(foo) as g:
    print g(1)
    print g(2)
print 'g count =',g.count
print 'f count =',f.count

with fcount2(f) as g:
    print g(1)
    print g(2)
print 'g count =',g.count
print 'f count =',f.count

with f:
    print f(1)
    print g(2)
print 'g count =',g.count
print 'f count =',f.count

是否还有其他一些参数(或不应该)传递给def 退出函数?

提问于
用户回答回答于
def __exit__(self, exc_type, exc_value, tb):
    if exc_type is not None:
        traceback.print_exception(exc_type, exc_value, tb)
        # return False # uncomment to pass exception through

    return True

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