将方法参数传递给类

debugcn 发表于 Dev

维沙尔·奈尔

我有以下可调用：

class SomeClass(object):

    def __init__(self, expr, return_status):

        self._expr = expr
        self._status = return_status


    def __call__(self):   

        if self._expr == self._status:
            return True

    def __str__(self):

        return ("Function: %s\n     Return Status: %s\n" %
                (self.__class__.__name__, self._status))

我面临的问题是，每当我尝试传递如下表达式时：

some_variable = SomeFunction(SomeClass.some_method,return_status=True)

SomeClass.some_method被评估并存储self._expr为布尔值。

我真正想要的是这个表达式 ( SomeClass.some_method) 被存储self._expr并在每次__call__(self)调用该方法时进行评估。

我说的有道理吗？

假设我正在举以下例子：

def addition(c,b):
        print "'addition' function called!\n"
        sum = c+b
        if sum>5:
            return True
        else:
            return False

    script_timeout = 3


    some_variable = SomeFunction(addition(1,2),return_status=True)

    print "some_variable: \n%s" %some_variable

    some_class.some_method(some_variable, script_timeout, 1)

这给了我以下输出：

'addition' function called!

SomeFunction (_init_) function called!

expr: False

self._expr = False and self._status = True

SomeFunction (_str_) function called!

self.__class__.__name__ = SomeFunction and self._expr = False

monitor: 
Function: SomeFunction
     Return Status of the Expression: True

SomeFunction (_call_) function called!

self._expr = False and self._status = True

SomeFunction (_call_) function called!

self._expr = False and self._status = True

SomeFunction (_call_) function called!

self._expr = False and self._status = True

因此，关注的是在SomeFunction 的每次迭代调用中都不会调用加法函数（通过some_method方法。）

所需的功能是SomeFunction（当被some_method调用时）应该调用函数加法。

资源中心

假设expr将是一个方法/函数并且假设您知道返回什么方法/函数，您有 3 个选项。只需遵循这 3 个选项中的一个，您就会实现您想要的。

1）您可以expr将分配调用到self.expr：

....
class CheckStatus:
    def __init__(self, expr, ...)
        self.expr = expr() # expr() being called here, store whatever the result is to self.expr

    def __call__(self):
        # self.expr already holds a boolean value, or anything your expr returns
        if self.expr == self.status:
            # self.expr match ...
            # do what else you have to do

obj = CheckStatus(SomeClass().method, ...) # pay attention how we pass the method here

2）如果self.expr是对那个的引用expr，那么：

class CheckStatus:
    def __init__(self, expr, ...):
        self.expr = expr

    def __call__(self):
        # in this example, self.expr now it's a reference to some method
        # thus you need to call self.expr here
        if self.expr() == self.status:
            ....

obj = CheckStatus(SomeClass().method, ...) # pay attention how we pass method for this example

3)SomeClass().method()在实例化时调用CheckStatus()：

class CheckStatus:
    def __init__(self, expr, ...):
        self.expr = expr # for this example, expr already is a boolean or anything else some method/function returned

    def __call__(self):
        # don't need to call anything here
        if self.expr == self.status:
            ....

obj = CheckStatus(SomeClass().method(), ...) # because here we called SomeClass().method()

您必须在CheckStatus某个地方调用传递给类的方法/函数，否则您将永远无法检查该方法/函数的结果。希望很清楚。

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