1.7. Principles for Code Quality

1.7.1. The Law of Demeter

It’s also known as the Principle of Least Knowledge, saying that an object should only communicate with its immediate neighbors, avoiding to access deeper and deeper objects.

See below for a small example how we would violate and obey the Law of Demeter.

# Bad Example
class Department:
    def __init__(self, manager):
        self.manager = manager

    def get_manager_name(self):
        # Bad: Accessing a method of an object deep within the hierarchy
        return self.manager.employee.name

class Employee:
    def __init__(self, name):
        self.name = name

class Manager:
    def __init__(self, employee):
        self.employee = employee

# Good Example
class Department:
    def __init__(self, manager):
        self.manager = manager
    
    def get_manager_name(self):
        # Good: Not going deeper
        return self.manager.get_name()

class Employee:
    def __init__(self, name):
        self.name = name

class Manager:
    def __init__(self, employee):
        self.employee = employee

    def get_name(self):
        return self.employee.name