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from abc import abstractmethod

from enum import Enum

class Relationship(Enum):

PARENT = 0

CHILD = 1

SIBLING = 2

class Person:

def __init__(self, name):

self.name = name

class RelationshipBrowser:

@abstractmethod

def find_all_children_of(self, name): pass

class Relationships(RelationshipBrowser): # low-level

relations = []

def add_parent_and_child(self, parent, child):

self.relations.append((parent, Relationship.PARENT, child))

self.relations.append((child, Relationship.PARENT, parent))

def find_all_children_of(self, name):

for r in self.relations:

if r[0].name == name and r[1] == Relationship.PARENT:

yield r[2].name

class Research:

# dependency on a low-level module directly

# bad because strongly dependent on e.g. storage type

# def __init__(self, relationships):

# # high-level: find all of john's children

# relations = relationships.relations

# for r in relations:

# if r[0].name == 'John' and r[1] == Relationship.PARENT:

# print(f'John has a child called {r[2].name}.')

def __init__(self, browser):

for p in browser.find_all_children_of("John"):

print(f'John has a child called {p}')

parent = Person('John')

child1 = Person('Chris')

child2 = Person('Matt')

# low-level module

relationships = Relationships()

relationships.add_parent_and_child(parent, child1)

relationships.add_parent_and_child(parent, child2)

Research(relationships)