Python：实例没有属性
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Python: instance has no attribute
提问by Mantas Marcinkus
I have a problem with list within a class in python. Here's my code :
我在 python 类中的列表有问题。这是我的代码：
class Residues:
def setdata(self, name):
self.name = name
self.atoms = list()
a = atom
C = Residues()
C.atoms.append(a)
Something like this. I get an error saying:
像这样的东西。我收到一条错误消息：
AttributeError: Residues instance has no attribute 'atoms'
采纳答案by NullUserException
Your class doesn't have a __init__(), so by the time it's instantiated, the attribute atomsis not present. You'd have to do C.setdata('something')so C.atomsbecomes available.
您的类没有__init__()，因此在实例化时，该属性atoms不存在。你必须这样C.setdata('something')做C.atoms变得可用。
>>> 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
>>>
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.
不像在 Java 这样的语言中，您在编译时就知道对象将具有哪些属性/成员变量，而在 Python 中，您可以在运行时动态添加属性。这也意味着同一类的实例可以具有不同的属性。
To ensure you'll always have (unless you mess with it down the line, then it's your own fault) an atomslist you could add a constructor:
为了确保您始终拥有一个atoms列表（除非您将其弄乱，否则这是您自己的错）您可以添加一个构造函数：
def __init__(self):
self.atoms = []
