I have this class:

class A(str):            
    def __str__(self):
        return "the string"
    
    def __repr__(self):
        return "the repr"

a = A("change me")

Running print a returns the string

Running repr(a) returns the repr

Running a returns change me

The problem

Running the instance a returns the string used to instantiate the class. How can I change this string in the instance after instantiation?

The returns of __str__ and __repr___ are not the problem, as in certain situations rather than calling these methods the instance is called directly. So where you may expect __repr__ to return, the instance returns the instantiation string instead.

I have been unable to find any attributes within the string class to change this. Most solutions I've tried require you to re-instance the a variable, which I don't want to do. I want to change the string from within the current instance of the object class variable.

I have tried rebuilding the class through methods utilising __new__ and type(). However, this seems to require re-instancing the stored class variable, as recreating the class creates a duplicate and does not update the current instance.

I am limited to using Python 2.7, due to pipeline constraints.

CodePudding user response：

I have a potential answer, although it feels VERY bad and hacky.

class A(str):            
    def __str__(self):
        return "the string"

    def __repr__(self):
        return "the repr"
    
    def _instance_name(self):
        return [k for k, v in globals().items() if v is self]
    
    def change(self, new_string):
        name = self._instance_name()

        if name:
            globals()[name[0]] = type('A', (A, ), self.__dict__)(new_string)

a = A("change me")

Running a returns change me

a.change("I have changed")

Running a returns I have changed

Changing globals this way feels like welcoming the end times, but it's the only solution I've found so far. Any other potential methods would be appreciated!