关于python class： callerRef的问题

Python code:

class A:
def __init__(self):
self.B_Handle = B_Handle
self.VA = "A_init"
print "Class A init"
def __getattr__(self, name):
print "A.__getattr__"
print "name=%s" % name
def callref(self, callref="A",):
print "A.callref = %s" % callref
return self.B_Handle.callref(self, callref)
class B:
def __init__(self):
self.VB = "B_init"
print self.VB
def callref(self, [color=#FF0000]callerRef,[/color] callref):
print "B.callref = %s" % callref
B_Handle = B()

if __name__ == "__main__":
print "eval callerRef start"
a = A()
a.callref()


运行结果：
>>> B_init
eval callerRef start
Class A init
A.callref = A
B.callref = A

看到一段这样的代码， 对其中的callerRef不是很理解，请高手指点！

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重发class B 代码：
Python code:

class B:
def __init__(self):
self.VB = "B_init"
print self.VB
def callref(self, [color=#FF0000]callerRef,[/color] callref):
print "B.callref = %s" % callref

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