Question

我想知道是否有办法在某些特定情况下配置一个返回False的类。是什么让空字符串和空列表返回False？如何使用我自己的条件重现该模式（例如，当该类的属性等于定义的值时返回False？）

举例说明我正在寻找的内容：

class Foo():
  def__init__(self, value):
    self.value=value

# I would like that the class Foo return False if his value equal 0.

a = Foo(1)
b = Foo(0)

for each in [a,b]:
  if each : print( "The value isn't 0 :)" )
  else : print( "The value is 0..." )

Answer 1

对于Python 3，您需要__bool__方法。对于Python 2，您需要__nonzero__。

class Foo():
  def __init__(self, value):
    self.value = value

  def __bool__(self):
    return self.value != 0

a = Foo(1)
b = Foo(0)

for each in [a,b]:
  if each : print( "The value isn't 0 :)" )
  else : print( "The value is 0..." )

Answer 2

像这样实施__bool__方法。

def __bool__(self):
    return flag
    # the flag is derived from the state of some attributes
    # which reflects the semantics of the object being truthy / falsy

在某些已定义的情况下，使用类返回False

2 个答案: