How to check if class instance exists in a list of class instance objects?

[buran]

If need to keep order buran dictionary(3.6+) will do that.

not sure if that's at me, but what I wanted to say is that given list [person1, person2, person3] if we use dict, at the end we will have
[person3, person2] (in that order in python 3.6, and [possibly] reversed in python2 and python3 before 3.6), i.e. person3 would replace person1 as value for key 'John'.