Question

即使更改对象属性self.name和self.author后，我也无法理解self.details为什么打印同一行。

class Book(object):
    def __init__(self, name, author):
        self.name = name
        self.author = author
        self.details = self.name + ' written by ' + self.author

bk = Book("Harry Potter", "J K Rowling")
print(bk.name)
print(bk.author)
print(bk.details)   #Harry Potter written by J K Rowling

bk.name = 'Becoming'
bk.marks= 'Michelle Obama'
print(bk.name)
print(bk.author)
print(bk.details)   #Harry Potter written by J K Rowling

Answer 1

因为details是从原始值创建的。串联后，它完全独立于其他值。如果要使用name / author的当前值来动态构造字符串，则use a property会在访问时动态计算details（根本不将其存储为属性）：

class Book(object):
    def __init__(self, name, author):
        self.name = name
        self.author = author
        # Don't make a `details` attribute at all

    @property
    def details(self):
        # This method is called whenever you refer to `somebook.details`
        return self.name + ' written by ' + self.author

Answer 2

self.details会在创建self.details = self.name + ' written by ' + self.author时创建并设置一次，但没有链接。 +操作只是对字符串进行串联。

确切地说，在您的第一个示例中，Python读取了self.details = self.name + ' written by ' + self.author，所以它读取了self.details = "Harry Potter" + ' written by ' + "J K Rowling"，所以self.details = "Harry Potter written by J K Rowling"

它只是一个以字符串为值的属性。在您明确更改之前，该字符串将保持不变。

如果您想要这种行为，则可以研究getter和setter，并为self.name和self.author创建一个setter，以自动更新self.details

为什么即使合并原始属性也不会更改通过合并其他属性创建的实例属性

2 个答案: