首先,@propertThe role is to put the method in the class『變成』了屬性,Easy to access by instance.propertThere are two usages：You can turn a method into a read-only property;Some properties can be filtered.
想象這樣一個場景,after instantiating a class,A property of the class needs to be assigned a value,At this time, the value assigned to the attribute attribute is not judged,If the property is given an inappropriate value,Then the code will report an error when it is executed later,為了避免這種情況,可以有兩種方法解決.
class Student():
def get_score(self):
return self._score
def set_score(self, value):
if not isinstance(value, int):
raise ValueError('score must be an integer!')
if value < 0 or value > 100:
raise ValueError('score must between 0 ~ 100!')
self._score = value
if __name__ == '__main__':
s = Student()
s.set_score(value="88")
print(s.get_score())
再Student類中,為了避免直接對 _score 屬性操作,我們提供了 get_score 和 set_score 方法,這樣起到了封裝的作用,把一些不想對外公開的屬性隱蔽起來,而只是提供方法給用戶操作,在方法裡面,我們可以檢查參數的合理性等.這樣做沒什麼問題,But we have an easier way to do it.
class Teacher():
@property
def score(self):
return self._score
@score.setter
def score(self, value):
if not isinstance(value, int):
raise ValueError('score must be an integer!')
if value < 0 or value > 100:
raise ValueError('score must between 0 ~ 100!')
self._score = value
if __name__ == '__main__':
t = Teacher()
t.score = 10
print(t.score)
t.score = 20
print(t.score)
在上面,我們給方法 score 加上了 @property,於是我們可以把 score 當成一個屬性來用,此時,A new decorator is created again score.setter,它可以把被裝飾的方法變成屬性來賦值.
另外,We don't have to use either score.setter 這個裝飾器,這時 score It becomes a read-only property：
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class test():
def __init__(self, s1):
self.s = s1
@property
def f1(self):
return self.s
if __name__ == '__main__':
t1 = test(s1=90)
print(t1.f1)
注意：last lineprint(t1.f1)不要加括號,print(t1.f1()),要不會報錯’int’ object is not callable
