Python中的特殊方法以及应用详解

# vector.py
from math import hypot

class Vector:
  def __init__(self, x=0, y=0):
    self.x = x
    self.y = y

  def __repr__(self):
    return f'Vector({self.x}, {self.y})'

  def __abs__(self):
    return hypot(self.x, self.y)

  def __bool__(self):
    return bool(self.x or self.y)

  def __add__(self, other):
    return Vector(self.x + other.x, self.y + other.y)

  def __mul__(self, scalar):
    return Vector(self.x * scalar, self.y * scalar)

# myclass.py
class MyClass:
  def __repr__(self):
    return 'MyClass'

  def __str__(self):
    return 'This is an instance of MyClass'

>>> from myclass import MyClass
>>> my = MyClass()
>>> my
MyClass
>>> print(my)
This is an instance of MyClass

# boolclass.py
class BoolClass:
  def __init__(self):
    self.list = []

  def add(self, item):
    self.list.append(item)

  def __len__(self):
    return len(self.list)

>>> from boolclass import BoolClass
>>> b = BoolClass()
>>> len(b)
0
>>> bool(b)
False
>>> b.add(1)
>>> len(b)
1
>>> bool(b)
True

# boolclass.py
class BoolClass:
  def __init__(self):
    self.list = []

  def add(self, item):
    self.list.append(item)

  def __len__(self):
    return len(self.list)

  def __bool__(self):
    return bool(sum(self.list))

>>> from boolclass import BoolClass
>>> b = BoolClass()
>>> b.add(1)
>>> len(b)
1
>>> bool(b)
True
>>> b.add(-1)
>>> len(b)
2
>>> bool(b)
False