python中的未绑定变量

Question

我试图用python制作一个玩具singleton来学习该语言的来龙去脉，但遇到了python如何工作的问题。我这样宣布班级

class ErrorLogger:
  # Singleton that provides logging to a file  
  instance = None

  def getInstance():
    # Our singleton "constructor"
    if instance is None :
      print "foo"

当我叫它

^{pr2}$

我明白了

 File "/home/paul/projects/peachpit/src/ErrorLogger.py", line 7, in getInstance
    if instance is None :
 UnboundLocalError: local variable 'instance' referenced before assignment

这是怎么回事，实例不应该被静态地赋值为Null吗？正确的方法是什么？在

Answer 1

您必须使用ErrorLogger前缀来调用它，因为它是一个静态变量。在

class ErrorLogger:
  # Singleton that provides logging to a file  
  instance = None

  @staticmethod
  def getInstance():
    # Our singleton "constructor"
    if ErrorLogger.instance is None :
      print "foo"