Sorting Through Data: Using Custom Classes and Comparators in Python Maps

Welcome to our exploration of sorted maps using custom classes and comparators in Python. In today's lesson, we'll learn how to use custom classes as keys in sorted maps. This approach enhances data organization and access. With the addition of comparators, we can dictate the order in such maps.

A sorted map is a dictionary with its keys always in order. This arrangement makes operations like searching for keys within a range more efficient. In Python, we use the SortedDict class from the sortedcontainers library to create sorted maps:

from sortedcontainers import SortedDict

s_map = SortedDict({'a': 1, 'b': 2, 'c': 3})
print(s_map)  # Outputs SortedDict({'a': 1, 'b': 2, 'c': 3})

Custom classes enable us to create objects that fit our data — for instance, a "Person" class for employee information or a "Book" class for a library database. In Python, classes are the blueprints for creating objects.

Consider this simple class, for example:

from sortedcontainers import SortedDict

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

person = Person("John Doe", 30)
print(person.name)  # Outputs "John Doe"
print(person.age)   # Outputs 30

Using custom classes as map keys helps organize complex multivariate keys in a sorted map. Below is an example of how to use comparators to dictate the order when using custom classes as keys:

from sortedcontainers import SortedDict

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

    def __hash__(self):
        return hash((self.name, self.score))

people = SortedDict()

john = Person("John", 30)
alice = Person("Alice", 25)

people[john] = "Programmer"
people[alice] = "Designer"

In this example, John is assigned the value "Programmer", and Alice is assigned the value "Designer". However, this code doesn't work, can you guess why?