Can You Override Python\'s Special Methods Directly on Instances?

Overriding Special Methods on Instance Objects

In Python, special methods with names surrounded by double underscores are typically not invoked on instances but rather on their classes. This is an implementation detail of CPython, the standard interpreter. Consequently, it is not possible to override __repr__() directly on an instance and expect the custom implementation to be used.

For instance, consider the following code:

class A(object):
    pass

def __repr__(self):
    return "A"

from types import MethodType
a = A()
print(a)   # Output: <__main__.A object at 0x0101C5D0>
print(repr(a))  # Output: '<__main__.A object at 0x0101C5D0>'

As we can see, repr(a) does not yield the expected result of "A."

To work around this limitation, one must define a new method that calls the original implementation, as follows:

class A(object):
    def __repr__(self):
        return self._repr()
    def _repr(self):
        return object.__repr__(self)

Now, you can override __repr__() on an instance by replacing _repr():

setattr(a, "_repr", MethodType(my_repr, a, a.__class__))

where my_repr is the desired custom implementation.

The above is the detailed content of Can You Override Python\'s Special Methods Directly on Instances?. For more information, please follow other related articles on the PHP Chinese website!