如何在脚本执行期间更改类的 __eq__

Question

<!-- language: lang-py -->

class File:
    ### Сlass initialization
    def __init__(self, path, name, size, date):
        self.path = path
        self.name = name
        self.size = size
        self.date = date

    def __eq__(self, other):
        # if self.name == other.name and self.size == other.size and self.date == other.date:
        if self.name == other.name and self.size == other.size:
        # if self.size == other.size and self.date == other.date:
            return True**

How change ( eq ) of class during script execution?

    def __eq__(self, other):
        # if self.name == other.name and self.size == other.size and self.date == other.date:
        if self.name == other.name and self.size == other.size:
        # if self.size == other.size and self.date == other.date:
        return True

Different variants must be triggered when certain conditions occur

Answer 1

Well, this is certainly possible:

class Foo(object):
    def __init__(self, x):
        self.x = x

    def __eq__(self, other):
        return other.x == self.x

foo1 = Foo(1)
foo2 = Foo(2)

print (foo1 == foo2)

def new_eq(self, other):
    return other.x - 1 == self.x

Foo.__eq__ = new_eq

print (foo1 == foo2)

Explanation:

__eq__ is an attribute of the class Foo , and it's a function bound to the class (a class method). You can set the __eq__ attribute to a new function to replace it. Note that because this is modifying the class, all instances see a change, including foo1 and foo2 that are already instantiated.

All that said, this is a pretty sketchy practice, especially for something like __eq__ , so I want to say that this is probably not a good solution to your problem, but not knowing what that problem is, I'll just say that if I were to see this sort of thing in code, it would make me rather nervous.

Answer 2

Instead of swapping __eq__ out on the fly, why not use the conditions to determine which case to use when __eq__ is called?

class Foo:
    def __eq__(self, other):
        if (self._condition_1):
            return self._eq_condition_1(other)
        elif (self._condition_2):
            return self._eq_condition_2(other)
        else:
            return self._eq_condition_default(other)

    def _eq_condition_1(self, other):
        return True

    def _eq_condition_2(self, other):
        return False

    def _eq_condition_default(self, other):
        return True