奇怪的Python的功能範圍的行爲

Question

我很困惑這個範圍的行爲：

class Bar: 
    def __init__(self): 
     for fn in ["open","openW","remove","mkdir","exists","isdir","listdir"]: 
      print "register", fn 
      def func_wrapper(filename): 
       print "called func wrapper", fn, filename 
      setattr(self, fn, func_wrapper) 

bar = Bar() 
bar.open("a") 
bar.remove("b") 
bar.listdir("c") 

這使輸出：

register open 
register openW 
register remove 
register mkdir 
register exists 
register isdir 
register listdir 
called func wrapper listdir a 
called func wrapper listdir b 
called func wrapper listdir c 

但我會預計func_wrapper將永遠是正確的功能。我知道func_wrapper的範圍是整個函數，但我在每次循環迭代中重新定義它，並且最後一個實例被保存在屬性中。我也試着在setattr下面添加func_wrapper = None，但這並沒有幫助（也想知道我......）。

我瞎了嗎？我甚至不知道如何解決這個問題。

Answer 1

要麼與

class Bar: 
    def __init__(self): 
     for fn in ["open","openW","remove","mkdir","exists","isdir","listdir"]: 
      print "register", fn 
      def func_wrapper(filename, fn=fn): 
       print "called func wrapper", fn, filename 
      setattr(self, fn, func_wrapper) 

，或者更魯棒，與

def mkwrapper(fn): 
    def func_wrapper(filename): 
     print "called func wrapper", fn, filename 
    func_wrapper.__name__ = fn 
    return func_wrapper 

class Bar: 
    def __init__(self): 
     for fn in ["open","openW","remove","mkdir","exists","isdir","listdir"]: 
      print "register", fn 
      func_wrapper = mkwrapper(fn) 
      setattr(self, fn, func_wrapper) 

在原來的實例中，所有生成的函數訪問相同的外部變量fn，這改變了在每一個循環運行。在修正的例子中，這是被阻止的。