Read only Property
===================



property 函数
------------

ref
------

Phillips_2010_python3_object

https://docs.python.org/2.7/library/functions.html#property

```python
class Parrot(object):
    def __init__(self):
        self._voltage = 100000

    # getter
    @property
    def voltage(self):
        """Get the current voltage."""
        return self._voltage
        
    # @voltage.setter
    # def voltage(self, volt):
    #     self._voltage = volt

a = Parrot()

print(a.voltage)
a.voltage = 1000  # 此句非法， 因为没有定义 set

print(a.voltage)
```