Question

我想知道为什么在这个代码中append()似乎在循环内部起作用，但是生成的xml仅显示最后一次迭代的修改，而remove()按预期工作。这是一个过于简化的例子，我处理大块数据，需要将相同的子树附加到许多不同的父节点。

from lxml import etree

xml = etree.fromstring('<tree><fruit id="1"></fruit><fruit id="2"></fruit></tree>')
sub = etree.fromstring('<apple/>')

for i, item in enumerate(xml):
    item.append(sub)
    print('Fruit {} with sub appended: {}'.format(
        i, etree.tostring(item).decode('ascii')))

print('\nResulting tree after iterating through items with append():\n' +
    etree.tostring(xml, pretty_print=True).decode('ascii'))

for item in xml:
    xml.remove(item)

print('Resulting tree after iterating through items with remove():\n' +
    etree.tostring(xml, pretty_print=True).decode('ascii'))

当前输出：

Fruit 0 with sub appended: <fruit id="1"><apple/></fruit>
Fruit 1 with sub appended: <fruit id="2"><apple/></fruit>

Resulting tree after iterating through items with append():
<tree>
  <fruit id="1"/>
  <fruit id="2">
    <apple/>
  </fruit>
</tree>

Resulting tree after iterating through items with remove():
<tree/>

在使用append() 的项目进行迭代后，的预期输出：

<tree> <fruit id="1"/> <apple/> </fruit> <fruit id="2"> <apple/> </fruit> </tree>

Answer 1

那是因为你只创建了一个<apple/>的实例来追加。所以基本上你只是将一个实例从一个父实例移动到另一个实例，直到最后append(sub)执行。尝试在<apple/>循环中移动创建for元素：

for i, item in enumerate(xml):
    sub = etree.fromstring('<apple/>')
    item.append(sub)
    print('Fruit {} with sub appended: {}'.format(
        i, etree.tostring(item).decode('ascii')))
print()

输出

Resulting tree after iterating through items with append():
<tree>
  <fruit id="1">
    <apple/>
  </fruit>
  <fruit id="2">
    <apple/>
  </fruit>
</tree>

来自循环的lxml.etree._Element.append（）不能按预期工作

1 个答案: