如何将值从类传递到类 - Python

Question

I am trying to pass a value from one function in a class to another function in a class. Below is some simplified code of what I'm trying to achieve.

class test:
    def __init__(self):
        self.differentvalue = 0
    def set(self, value):
        print(value)
        self.differentvalue = value #this is not the same value as defined above - i.e. this is a new variable created in foo class i believe

class foo:
    def __init__(self):
        test.set(self, 5)

if __name__ == '__main__':
    foo()

I do not want __init__ to be called so test().set(5) is not an option.

Cheers, Sean

Answer 1

You have two options

Option #1, best option if you need to keep a different context for differtvalue for each instance of Test

class Test:

    def __init__(self):
        self.differentvalue = 0

    def set(self, value):
        self.differentvalue = value

class foo:
    def __init__(self):
        test = Test()
        test.set(5)

Option #2, best if you need to keep the latest value for differentvalue across all Test classes

class Test:

    __DIFFERENTVALUE = 0

    def __init__(self):
        pass

    @staticmethod
    def set(value):
        Test.__DIFFERENTVALUE = value

class foo:
    def __init__(self):
        Test.set(5)

Answer 2

You could define a class variable with a value of None , then upon calling the setter for the first time, assign a value to it. Further calls to the setter will not change the value.

In the following example, an __init__ method is not required in Test .

class Test:

    differentvalue = None

    @classmethod
    def set(cls, value):
        if value is not None and Test.differentvalue is None:
            Test.differentvalue = value

class foo:
    def __init__(self):
        Test.set(5)

if __name__ == '__main__':
    foo()
    print(Test.differentvalue)
    Test.set(12)
    print(Test.differentvalue)

output:

5
5   # the value did not change