使用Python将xml声明写入文件

我通过循环字符串列表在python中编写多个xml文件.假设我有:

from xml.etree.ElementTree import ElementTree, Element, SubElement, tostring

parent = Element('parent')
child = SubElement(parent, 'child')
f = open('file.xml', 'w')
document = ElementTree(parent)
l = ['a', 'b', 'c']
for ch in l:
    child.text = ch
    document.write(f, encoding='utf-8', xml_declaration=True)

输出:

a
b
c

期望的输出:

a
b
c

我只希望xml声明出现在文件的顶部一次.可能应该在循环之前将声明写入文件,但是当我尝试这样时,我会得到空元素.我不想这样做:

f.write('')

如何只写xml声明到文件？

编辑:所需的输出

您需要在写入文件之前将SubItems添加到树中.在您的代码中,您覆盖了相同的元素,并在循环的每次迭代中编写了整个XML文档.

此外,您的XML语法缺少顶级"root"元素才有效.

from xml.etree.ElementTree import ElementTree, Element, SubElement, tostring

root = Element('root')

l = ['a', 'b', 'c']
for ch in l:
    parent = SubElement(root,'parent')
    child = SubElement(parent, 'child')
    child.text = ch

document = ElementTree(root)
document.write('file.xml', encoding='utf-8', xml_declaration=True)

输出将是:

  a
  b
  c