Question

我有这个xml输入文件：

<?xml version="1.0"?>
<zero>
  <First>
    <second>
      <third-num>1</third-num>
      <third-def>object001</third-def>
      <third-len>458</third-len>
    </second>
    <second>
      <third-num>2</third-num>
      <third-def>object002</third-def>
      <third-len>426</third-len>
    </second>
    <second>
      <third-num>3</third-num>
      <third-def>object003</third-def>
      <third-len>998</third-len>
    </second>
  </First>
</zero>

我的目标是删除<third-def>不是值的任何第二级。为此，我写了这段代码：

try:
    import xml.etree.cElementTree as ET
except ImportError:
    import xml.etree.ElementTree as ET
inputfile='inputfile.xml'
tree = ET.parse(inputfile)
root = tree.getroot()

elem = tree.find('First')
for elem2 in tree.iter(tag='second'):
    if elem2.find('third-def').text == 'object001':
        pass
    else:
        elem.remove(elem2)
        #elem2.clear()

我的问题是elem.remove(elem2)。它会跳过其他所有第二级。以下是此代码的输出：

<?xml version="1.0" ?>
<zero>
  <First>
    <second>
      <third-num>1</third-num>
      <third-def>object001</third-def>
      <third-len>458</third-len>
    </second>
    <second>
      <third-num>3</third-num>
      <third-def>object003</third-def>
      <third-len>998</third-len>
    </second>
  </First>
</zero>

现在，如果我取消对elem2.clear()行的评论，那么该脚本可以正常运行，但输出不太好，因为它保留了所有已移除的第二级：

<?xml version="1.0" ?>
<zero>
  <First>
    <second>
      <third-num>1</third-num>
      <third-def>object001</third-def>
      <third-len>458</third-len>
    </second>
    <second/>
    <second/>
  </First>
</zero>

有人知道为什么我的element.remove()陈述错了吗？

Answer 1

你正在循环实况树：

for elem2 in tree.iter(tag='second'):

然后在迭代时更改。＆＃39;计数器＆＃39;迭代的结果不会被告知有关元素数量的变化，因此当查看元素0并删除该元素时，迭代器将继续移动到元素编号1.但是是元素编号1现在是元素编号0。

首先捕获所有元素的列表，然后循环遍历：

for elem2 in tree.findall('.//second'):

.findall()会返回结果列表，在您更改树时不会更新。

现在迭代不会跳过最后一个元素：

>>> print ET.tostring(tree)
<zero>
  <First>
    <second>
      <third-num>1</third-num>
      <third-def>object001</third-def>
      <third-len>458</third-len>
    </second>
    </First>
</zero>

这种现象不仅限于ElementTree树;见Loop "Forgets" to Remove Some Items

ElementTree：Element.remove（）跳跃迭代

1 个答案: