Python check if object is in list of objects

Question

I have a list of objects in Python. I then have another list of objects. I want to go through the first list and see if any items appear in the second list.

I thought I could simply do

for item1 in list1:     for item2 in list2:         if item1 == item2:             print "item %s in both lists" 

However this does not seem to work. Although if I do:

if item1.title == item2.title: 

it works okay. I have more attributes than this though so don't really want to do 1 big if statement comparing all the attributes if I don't have to.

Can anyone give me help or advise on what I can do to find the objects which appear in both lists.

Thanks

Answer 1

Assuming that your object has only a title attribute which is relevant for equality, you have to implement the __eq__ method as follows:

class YourObject:     [...]     def __eq__(self, other):         return self.title == other.title 

Of course if you have more attributes that are relevant for equality, you must include those as well. You might also consider implementing __ne__ and __cmp__ for consistent behaviour.

Answer 2

In case the objects are not the same instance, you need to implement the __eq__ method for python to be able to tell when 2 objects are actually equal.

Of course that most library types, such as strings and lists already have __eq__ implemented, which may be the reason comparing titles works for you (are they strings?).

For further information see the python documentation.
Here is a random example for __eq__.