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

[buran]

You need to implement some special methods in your class. Here is a quick example

class Person():
    def __init__(self, name):
        self.name = name
        
    def __eq__(self, other):
        return (self.name, ) == (other.name, )
        
    def __hash__(self):
        return hash((self.name,))
        
    def __str__(self):
        return self.name
        

    
person1 = Person('John')
person2 = Person('Allice')
person3 = Person('John')

persons = [person1, person2, person3]
print(persons)
for person in persons:
    print(person)

unique_persons = set(persons)
print(unique_persons)
for person in unique_persons:
    print(person)

Output:
[<__main__.Person instance at 0x02FB1B20>, <__main__.Person instance at 0x02FB53F0>, <__main__.Person instance at 0x02FB5418>]
John
Allice
John
set([<__main__.Person instance at 0x02FB1B20>, <__main__.Person instance at 0x02FB53F0>])
John
Allice
>>>

note that I have added __str__() just for more clarity in the example output

---

if for some reason you don't want/are not able to change the class

class Person():
    def __init__(self, name):
        self.name = name
         
    def __str__(self):
        return self.name
     
person1 = Person('John')
person2 = Person('Allice')
person3 = Person('John')
 
persons = [person1, person2, person3]
print(persons)
for person in persons:
    print(person)
 
def dedup(persons):
    unique = []
    unique_names = set()
    for person in persons:
        if person.name not in unique_names:
            unique.append(person)
            unique_names.add(person.name)
    return unique
    
unique_persons = dedup(persons)
print(unique_persons)
for person in unique_persons:
    print(person)

Output:
[<__main__.Person instance at 0x02FD1E40>, <__main__.Person instance at 0x02FD53A0>, <__main__.Person instance at 0x02FD53C8>]
John
Allice
John
[<__main__.Person instance at 0x02FD1E40>, <__main__.Person instance at 0x02FD53A0>]
John
Allice
>>>