Python：实例没有属性 [英] Python: instance has no attribute

问题描述

我在Python中的类中有一个问题。这是我的代码：

I have a problem with list within a class in python. Here's my code :

class Residues:
    def setdata(self, name):
        self.name = name
        self.atoms = list()

a = atom
C = Residues()
C.atoms.append(a)

这样的东西。我得到一个错误说：

Something like this. I get an error saying:

AttributeError: Residues instance has no attribute 'atoms'

推荐答案

您的类没有 __ init __（），所以在实例化的时候，属性 atoms 不存在。你必须做 C.setdata（'something'）所以 C.atoms 变得可用。

Your class doesn't have a __init__(), so by the time it's instantiated, the attribute atoms is not present. You'd have to do C.setdata('something') so C.atoms becomes available.

>>> C = Residues()
>>> C.atoms.append('thing')

Traceback (most recent call last):
  File "<pyshell#84>", line 1, in <module>
    B.atoms.append('thing')
AttributeError: Residues instance has no attribute 'atoms'

>>> C.setdata('something')
>>> C.atoms.append('thing')   # now it works
>>> 

与Java类似的语言不同，在编译时你知道对象会有什么属性/成员变量，在Python中，您可以在运行时动态添加属性。这也意味着同一个类的实例可以有不同的属性。

Unlike in languages like Java, where you know at compile time what attributes/member variables an object will have, in Python you can dynamically add attributes at runtime. This also implies instances of the same class can have different attributes.

为了确保你总是有（除非你把它弄乱了，那么它是你自己的错误） atoms 列表，您可以添加一个构造函数：

To ensure you'll always have (unless you mess with it down the line, then it's your own fault) an atoms list you could add a constructor:

def __init__(self):
    self.atoms = []

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