Pythonの演算子オーバーロード

Python 中級オブジェクト指向プログラミング

Jake Roach

Data Engineer

比較演算子のオーバーロード

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

  def __eq__(self, other):
      return self.name == other.name

==の振る舞いをカスタマイズ

マジックメソッド__eq__()を使う
引数はselfとother
真偽値を返す

bryce = Person("Bryce")
orion = Person("Orion")
print(bryce == orion)

False

chuck = Person("Charles Carmichael")
charles = Person("Charles Carmichael")
print(chuck == charles)

True

2つのオブジェクトを足す

class Team:
  def __init__(self, team_members):
      self.team_members = team_members

# Create two Team objects, attempt to add them
rookies = Team(["Casey", "Emmitt"])
veterans = Team(["Mike", "Chuck"])
dream_team = rookies + veterans

Traceback (most recent call last):
  File "<stdin>", line 8, in <module>
TypeError: unsupported operand type(s) for +: 'Team' and 'Team'

+ 演算子のオーバーロード

class Team:
  def __init__(self, team_members):
    # team_members is a list of names
    self.team_members = team_members

  def __add__(self, other):
    # Adding Team objects creates a larger Team
    return Team(self.team_members + other.team_members)

マジックメソッド__add__()で+をオーバーロード
__add__()にはselfとotherが渡される
足し算するオブジェクトのteam_membersを結合して新しいTeamを作る

2つのオブジェクトを足す

# Create two Team objects
rookies = Team(["Casey", "Emmitt"])
veterans = Team(["Mike", "Chuck"])

# Attempt to add these two Teams together
dream_team = rookies + veterans
print(type(dream_team))
print(dream_team.team_members)

Team
["Casey", "Emmitt", "Mike", "Chuck"]

+で新しい型のオブジェクトを作る

class Team:
  def __init__(self, team_members):
      self.team_members = team_members

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

  def __add__(self, other):
    # Use the + operator to create a
    # Team with the name of each Employee
    return Team([self.name, other.name])

Employee同士を組み合わせてTeamを作りたい場合は？

__add__をEmployeeクラスに実装する
Employee名のリストから新しいTeamを作成
2つのEmployeeを足すと1つのTeamになる

2つのオブジェクトを足して新しいオブジェクトを作成

# Create two Employee objects
anna = Employee("Anna", "Technical Specialist")
jeff = Employee("Jeffrey", "Musician")

# Now, attempt to add these together to create a team
audio_team = anna + jeff
print(type(audio_team))
print(audio_team.team_members)

Team
["Anna", "Jeffrey"]

他の演算子のオーバーロード

Operator	Magic Method	Operator Type
-	`__sub__`	Arithmetic
!=	`__ne__`	Comparison
<	`__lt__`	Comparison
>	`__gt__`	Comparison
+=	`__iadd__`	Assignment
and	`__and__`	Logical
in	`__contains__`	Membership
is	`__is__`	Identity

…ほかにも多数！

Passons à la pratique !

Python 中級オブジェクト指向プログラミング