为什么 bool(xml.etree.ElementTree.Element) 评估为 False?

2022-01-19 00:00:00 python boolean

问题描述

import xml.etree.ElementTree as ET
e = ET.Element('Brock',Role="Bodyguard")
print bool(e)

为什么 xml.etree.ElementTree.Element 被认为是 False?

Why is an xml.etree.ElementTree.Element considered False?

我知道我可以执行 if e is not None 来检查是否存在.但我强烈希望 bool(e) 返回 True.

I know that I can do if e is not None to check for existence. But I would strongly expect bool(e) to return True.

解决方案

事实证明，如果 Element 对象没有子对象，则将其视为 False 值.

As it turns out, Element objects are considered a False value if they have no children.

我在源代码中找到了这个:

I found this in the source:

def __nonzero__(self):
    warnings.warn(
        "The behavior of this method will change in future versions.  "
        "Use specific 'len(elem)' or 'elem is not None' test instead.",
        FutureWarning, stacklevel=2
        )
    return len(self._children) != 0 # emulate old behaviour, for now

即使是内联评论也同意你的看法——这种行为是有问题的；)

Even the inline comment agrees with you -- this behavior is iffy ;)

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