從循環lxml.etree._Element.append（）不按預期工作

Question

我想知道爲什麼在此代碼append()似乎從循環內部工作，但生成的xml顯示修改只從最後一次迭代，而remove()按預期工作。這是一個過分簡化的例子，我正在處理大量的數據，並且需要將相同的子樹附加到許多不同的父母身上。

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')) 

電流輸出：

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/> 

從 通過項目與append()迭代後

預期輸出：

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

Answer 1

那是因爲你只創建了一個實例被附加的<apple/> 。所以基本上你只是將一個實例從一個父母移到另一個父母，直到最後一個append(sub)執行完畢。嘗試for環路內移動<apple/>元素的創作，而不是：

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() 

輸出：

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