Question

I'm using a Class provided by a client (I have no access to the object code), and I'm trying to check if a object has a attribute. The attribute itself is write only, so the hasattr fails:

>>> driver.console.con.input = 'm'
>>> hasattr(driver.console.con, 'input')
False
>>> simics> @driver.console.con.input
Traceback (most recent call last):
File "<string>", line 1, in <module>
Attribute: Failed converting 'input' attribute in object   
'driver.console.con' to Python: input attribute in driver.console.con 
object: not readable.

Is there a different way to check if an attribute exists?

Answer 1

您似乎拥有某种将Python连接到扩展的本机代码代理，而且它违反了正常的Python惯例

有两种可能性：

driver.console.con对象有一个名称空间，它将属性实现为descriptors，而input描述符只有__set__ method（可能还有__delete__ method }）。在这种情况下，查找描述符：
```
if 'input' in vars(type(driver.console.con)):
    # there is an `input` name in the namespace
    attr = vars(type(driver.console.con))['input']
    if hasattr(attr, '__set__'):
        # can be set
        ...
```
此处vars() function检索用于driver.console.con的类的命名空间。
代理使用__getattr__（甚至__getattribute__）和__setattr__ hooks来处理任意属性。你在这里运气不好，你无法检测任何方法在hasattr()之外支持哪些属性并尝试直接设置属性。使用try...except保护：
```
try:
    driver.console.con.input = 'something'
except Attribute:   # exactly what exception object does this throw?
    # can't be set, not a writable attribute
    pass
```
您可能必须使用调试器或print()语句来确切地确定抛出的异常（使用try...except Exception as ex:块来捕获所有异常，然后检查ex）;在你的问题的追溯中，最后的异常消息看起来非常不标准。那个项目真的应该提高AttributeError。

考虑到抛出相当自定义的异常，我的钱在选项2上（但如果描述符上的__get__方法抛出异常，则选项1仍然存在）。

Python: Check for write only attr of a Class

1 个答案: