函數在類中的屬性

Question

我可以使用函數的屬性來設置狀態標志，例如

def Say_Hello():
    if Say_Hello.yet == True:
        print('I said hello already ...')
    elif Say_Hello.yet == False:
        Say_Hello.yet = True
        print('Hello!')

Say_Hello.yet = False

if __name__ == '__main__':
    Say_Hello()
    Say_Hello()

輸出是

Hello!
I said hello already ...

但是，當嘗試將該函數放入類中時，例如

class Speaker:
    def __init__(self):
        pass

    def Say_Hello(self):
        if self.Say_Hello.yet == True:
            print('I said hello already ...')
        elif self.Say_Hello.yet == False:
            self.Say_Hello.yet = True
            print('Hello!')

    Say_Hello.yet = False

if __name__ == '__main__':
    speaker = Speaker()
    speaker.Say_Hello()
    speaker.Say_Hello()

有這個錯誤：

Traceback (most recent call last):

  File "...func_attribute_test_class_notworking.py", line 16, in <module>
     speaker.Say_Hello()
  File "...func_attribute_test_class_notworking.py", line 9, in Say_Hello
    self.Say_Hello.yet = True
AttributeError: 'method' object has no attribute 'yet'

在類中使用函數屬性的正確方法是什么？

Answer 1

Speaker.Say_Hello和speaker.Say_Hello是兩個不同的對象。 前者是在class語句體中定義的函數：

>>> Speaker.Say_Hello
<function Speaker.Say_Hello at 0x1051e5550>

而后者是method一個實例：

>>> speaker.Say_Hello
<bound method Speaker.Say_Hello of <__main__.Speaker object at 0x10516dd60>>

此外，每次訪問speaker.Say_Hello ，都會獲得不同的method實例。

>>> speaker.Say_Hello is speaker.Say_Hello
False

你應該只使用self代替。 無論如何，函數屬性更像是一個沒有明確禁止的意外特性，而不是您應該使用的東西。

class Speaker:
    def __init__(self):
        self._said_hello = False

    def Say_Hello(self):
        if self._said_hello:
            print('I said hello already ...')
        else:
            self._said_hello = True
            print('Hello!')

如果您想跟蹤Speaker任何實例是否調用了它的Say_Hello方法，而不是單獨跟蹤每個實例，請使用類屬性。

class Speaker:
    _said_hello = False

    def Say_Hello(self):
        if self._said_hello:
            print('Someone said hello already ...')
        else:
            type(self)._said_hello = True
            print('Hello!')