python中的未绑定变量

Question

我正在尝试在python中制作一个玩具单例来学习语言的来龙去脉,并且遇到了python如何工作的问题.我宣布这样的课程

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

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

我打电话的时候

log = ErrorLogger.getInstance()

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

这里发生了什么,不应该静态分配Null？这样做的正确方法是什么？

Answer 1

你必须用ErrorLogger前缀来调用它,因为它是一个静态变量.

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

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