Python通过属性手段实现只允许调用一次的示例讲解

class DemoClass:
  def __init__(self):
    pass
  def AttrCheck(self):
    try:
      self.value
      print("already hasvalue")
      raise ValueAttrError
    except AttributeError:
      self.value = 0
      print(self.value)
 
obj = DemoClass()
obj.AttrCheck()
obj.AttrCheck()

grey@DESKTOP-3T80NPQ:/mnt/e/01_workspace/02_programme_language/03_python/03_OOP/2017/08$python attr1.py
0
already has value
Traceback (mostrecent call last):
 File "attr1.py", line 15, in<module>
 obj.AttrCheck()
 File "attr1.py", line 8, inAttrCheck
 raiseRuntimeError("multi-excued!")
RuntimeError:multi-excued!  

class DemoClass:
  def __init__(self):
    pass
  def AttrCheck(self,value):
    try:
      self.value
      print("already hasvalue")
      raiseRuntimeError("multi-excued!")
    except AttributeError:
      self.value = value
      print(self.value)
 
obj = DemoClass()
obj.AttrCheck(123)
obj.AttrCheck(123)

grey@DESKTOP-3T80NPQ:/mnt/e/01_workspace/02_programme_language/03_python/03_OOP/2017/08$python attr1.py
123
already has value
Traceback (mostrecent call last):
 File "attr1.py", line 15, in<module>
 obj.AttrCheck(123)
 File "attr1.py", line 8, in AttrCheck
 raiseRuntimeError("multi-excued!")
RuntimeError:multi-excued!