Compare object instances for equality by their attributes
equality, python
Solution
You should implement the method `__eq__`:
class MyClass:
def __init__(self, foo, bar):
self.foo = foo
self.bar = bar
def __eq__(self, other):
if not isinstance(other, MyClass):
# don't attempt to compare against unrelated types
return NotImplemented
return self.foo == other.foo and self.bar == other.bar
Now it outputs:
>>> x == y
True
Note that implementing `__eq__` will automatically make instances of your class unhashable, which means they can't be stored in sets and dicts. If you're not modelling an immutable type (i.e. if the attributes `foo` and `bar` may change the value within the lifetime of your object), then it's recommended to just leave your instances as unhashable.
If you are modelling an immutable type, you should also implement the data model hook `__hash__`:
class MyClass:
...
def __hash__(self):
# necessary for instances to behave sanely in dicts and sets.
return hash((self.foo, self.bar))
A general solution, like the idea of looping through `__dict__` and comparing values, is not advisable - it can never be truly general because the `__dict__` may have uncomparable or unhashable types contained within.
N.B.: be aware that before Python 3, you may need to use `__cmp__` instead of `__eq__`. Python 2 users may also want to implement `__ne__`, since a sensible default behaviour for inequality (i.e. inverting the equality result) will not be automatically created in Python 2.
Problem
I have a class `MyClass`, which contains two member variables `foo` and `bar`: ``` class MyClass: def __init__(self, foo, bar): self.foo = foo self.bar = bar ``` I have two instances of this class, each of which has identical values for `foo` and `bar`: ``` x = MyClass('foo', 'bar') y = MyClass('foo', 'bar') ``` However, when I compare them for equality, Python returns `False`: ``` >>> x == y False ``` How can I make Python consider these two objects equal?