Comparing two identical objects in Python (2.7) returns False

问题

I have a function in Python called object_from_DB. The definition isn't important except that it takes an ID value as an argument, uses the sqlite3 library to pull matching values from a table in a .db file, and then uses those values as arguments in the initialization of an object. The database is in no way changed by the use of this function.

This sample code, in light of this, baffles me.

>>> x = object_from_DB(422)
>>> y = object_from_DB(422)
>>> x == y
False

Why does this happen, and what sort of technique will cause x and y to return True when compared?

回答1:

By default, two distinct instances of any user-defined class are unequal:

>>> class X: pass
... 
>>> a = X()
>>> b = X()
>>> a == b
False

If you want different behaviour, you have to define it:

class Y:

    def __init__(self, value):
        self.value = value

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

>>> c = Y(3)
>>> d = Y(3)
>>> e = Y(4)
>>> c == d
True
>>> d == e
False

来源：https://stackoverflow.com/questions/37648137/comparing-two-identical-objects-in-python-2-7-returns-false