将方法参数传递给类

Question

I have the following callable:

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))

The problem I am facing is this that whenever I try to pass an expression like:

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

SomeClass.some_method gets evaluated and gets stored in self._expr as a boolean value.

What I actually want is this expression ( SomeClass.some_method ) be stored in self._expr and get evaluated each time the __call__(self) method is called.

Am I making sense?

Let's say I am taking the following example:

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)

This gives me the following output:

'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

So, the concern is the addition function is not getting called with each iteration calling of SomeFunction (by the some_method method.)

The required functionality is this that SomeFunction (when called by some_method ) should call the function addition .

Answer 1

Assuming expr will be a method/function and assuming you know what method/function returns, you have 3 options. Follow just one of these 3 options and you'll achieve what you want.

1) You can call expr in the assignement to 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) If self.expr is a reference to that expr , then:

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) call the SomeClass().method() at instantiation of 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()

You have to call the method/function your passing in to your CheckStatus class somewhere, otherwise you'll never have that method/function result to check. Hope it was clear.

Answer 2

class S(object):
    def __init__(self, expr, return_status):
        self._expr = expr
        self._status = return_status

    def __call__(self):   
        if self._expr() == self._status:
            raise Exception
        self._expr()

    def __str__(self):
        return ("Function: %s\n     Return Status of the Expression: %s\n" %
                (self.__class__.__name__, self._status))

def some_method():return True
try:
    S(some_method,return_status=True)()
except Exception as e:
    print('Got Exception')