>>> [] is None
False
>>> [] == None
False
>>> def foo(par=[]):
    if par is None:
        par = []
        par.append(0)
    print par

    
>>> foo()
[]
上面是我的测试结果，没有问题，if后面的语句不会被执行，还有参数最好不要用[]，请看：http://www.ferg.org/projects/python_gotchas.html#contents_item_6


  ----- Original Message ----- 
  From: 小楼听雨 
  To: python-chinese at lists.python.cn 
  Sent: Tuesday, August 09, 2005 7:54 PM
  Subject: Re: Re: [python-chinese] two questions


  def foo(par=[]):
      if par is None:
          par = []
          par.append(0)
      print par

  foo()
  print foo.func_defaults

  foo()
  print foo.func_defaults

  foo([9])
  print foo.func_defaults

  foo()
  print foo.func_defaults

  结果是：
  []         
  ([],) #为什么不是（[0]，）
  []
  ([],)
  [9]
  ([],)
  []
  ([],)
   难道是par.append(0)的问题？
  　　


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