CODEWITHSUNDEEP
pythonpython-3.xcallablecallable-object
tyleax
tyleax

Reputation: 1788

How to execute function if class instance is passed?

I currently have a TestClass that is callable. The callable executes a function that raises an exception if any attribute is equal to None. The purpose of defining it to be callable is so when TestClass instance is passed to another function or copied, it will perform a check that all attributes exist prior to being passed, else it will raise an exception.

The line below that exhibits this logic is UsesTestClass(testClass()).

Ideally I want to be able to perform the same check without having to "call" the class instance. For example, UsesTestClass(testClass). Is there a magic method or some other way to configure the class to be able to execute a function prior to being passed as an argument?

class TestClass:
    def __init__(self):
        self.name = None

    def run(self):
        if self.name is None:
            raise Exception("'name' attribute is 'None'")

    def __call__(self):
        self.run()
        return self

def UsesTestClass(testClass):
    print(testClass.name)

testClass = TestClass()
testClass.name = "Hello"
UsesTestClass(testClass())

Upvotes: 3

Views: 1351

Answers (1)

SafeDev
SafeDev

Reputation: 672

If you use the types library integrated into python you can do this.

import types


class TestClass:
    def __init__(self):
        self.name = None

    def __getattribute__(self, attr):
        method = object.__getattribute__(self, attr)
        if not method:
            raise Exception("Attribute %s not implemented" % attr)
        if type(method) == types.MethodType:
            self.run()
        return method

    def run(self):
        if self.name is None:
            raise Exception("'name' attribute is 'None'")

    def __call__(self):
        self.run()
        return self


def UsesTestClass(testClass):
    print(testClass.name)


testClass = TestClass()
testClass.name = "Hello"
UsesTestClass(testClass)

Upvotes: 1

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