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dependency_inversion.py
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dependency_inversion.py
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"""
Dependency Inversion Principle
- High level modules should not depend on low level ones
- Use abstractions
"""
from enum import Enum
from abc import abstractmethod
class Relationship(Enum):
PARENT = 0
CHILD = 1
SIBLING = 2
class Person:
def __init__(self, name):
self.name = name
# solution
class RelationshipBrowser():
@abstractmethod
def find_all_children(self, name):
pass
class Relationships(RelationshipBrowser):
# low level module
def __init__(self):
self.relations = []
def add_parent_and_child(self, parent, child):
self.relations.append(
(parent, Relationship.PARENT, child)
)
self.relations.append(
(child, Relationship.CHILD, parent)
)
# solution
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:
# high level module
# (old way)
# def __init__(self, relationships):
# 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}")
# solution
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')
RL = Relationships()
RL.add_parent_and_child(PARENT, CHILD1)
RL.add_parent_and_child(PARENT, CHILD2)
Research(RL)