How to return max of objects's sequence, where each objects have same fields with different values?

Question

Suppose, we have sequence of instances of one class. Let's describe class

class Person:
    def __init__(self, name, lastname):
        self.name = name
        self.lastname = lastname

Creating instances:

obj1 = Person('Andrew', 'Martin')
obj2 = Person('Mark', 'Levy')
obj3 = Person('Harry', 'Anderson')
objs = (obj1, obj2, obj3)

I want to return the maximum from the tuple in two fields. Something like the following:

from operator import attrgetter
max_obj = max(objs, key=(attrgetter('lastname'), attrgetter('name')))

Such code raise an error

(TypeError: 'tuple' object is not callable).

How, then, can one get the maximum?

Answer 1

You can concatenate these properties in the key using a lambda function:

max_obj = max(objs, key=lambda x: x.lastname.lower() + x.name.lower())

For instance:

obj1 = Person('George', 'Martin')
obj2 = Person('Beth', 'Martin')
obj3 = Person('Mark', 'Levy')
obj4 = Person('Harry', 'Anderson')
objs = (obj1, obj2, obj3, obj4)

from operator import attrgetter
max_obj = max(objs, key=lambda x: x.lastname.lower() + x.name.lower())
print(max_obj.name)

Out: George

More on using functions as keys for the max function can be found here.