英文:
How to avoid recursive error when returning python dict elements in python?
问题
以下是翻译好的代码部分：
假设你想将Python字典的元素作为类本身的属性返回，你可以这样实现：
class MyClass:
def __init__(self):
print(self.x)
self.metadata = {
"a": 42,
"b": 1,
}
def __getattr__(self, item):
if item in self.metadata:
return self.metadata[item]
else:
raise KeyError(f"No attribute {item} found.")
test = MyClass()
但是这个实现会创建一个递归错误。
英文:
Suppose you want to return elements of a python dictionary as attributes of the class itself, you might implement it as follows:
class MyClass:
def __init__(self):
print(self.x)
self.metadata = {
"a": 42,
"b": 1,
}
def __getattr__(self, item):
if item in self.metadata:
return self.metadata[item]
else:
raise KeyError(f"No attribute {item} found.")
test = MyClass()
But that implementation creates a recursive error.
答案1
得分: 1
代码部分不翻译。以下是翻译好的部分：
问题在于在__getattr__方法中，它检查字典self.metadata中是否存在某个元素item，但是self.metadata尚未定义！因此，通过获取属性self.metadata时，它再次调用__getattr__方法！
解决方法是首先检查metadata属性是否存在。因此，__getattr__方法将变为：
def __getattr__(self, item):
if "metadata" in self.__dict__ and item in self.metadata:
return self.metadata[item]
else:
raise KeyError(f"No attribute {item} found.")
因此，只有在类中存在属性metadata时，它才会检查item是否存在...
英文:
The problem here is that in the method __getattr__ it is checked if some element item is in the dict self.metadata which is not yet defined! So by getting the attribute self.metadata it calls the __getattr__ method again!
The solution is to check if the metadata attribute exists in the first place. So the __getattr__ method will become
def __getattr__(item):
if "metadata" in self.__dict__ and item in self.metadata:
return self.metadata[item]
else:
raise KeyError(f"No attribute {item} found.")
So only if the atribute metadata exists in the class it will check if the item exists...
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