python - 添加新元素后，lxml 库不向树添加换行符或缩进

Question

标题不言自明，在将其标记为重复之前，请考虑我已经检查了 this answer它对我不起作用，因为我什至没有在 sys.stdout 中获得正确的格式，不仅是在写入文件时。所以我有以下 xml (test.xml):

<?xml version="1.0" encoding="UTF-8"?>
<soap:Envelope xmlns:soap="http://www...">
  <soap:Body>
    <SubmitTransaction xmlns="http://www.">
      <Authentication>
      </Authentication>
      <Transaction>
        <DataFields>
        </DataFields>
      </Transaction>
    </SubmitTransaction>
  </soap:Body>
</soap:Envelope>

以及以下代码:

from lxml import etree

parser = etree.XMLParser(remove_blank_text=True)
tree = etree.parse("test.xml", parser)

def get_data_fields():
    for node in tree.iter():
        if 'DataFields' in node.tag:
            return node
a = get_data_fields()
field = etree.Element('Field_1')
child_1 = etree.Element('FieldName')
child_2 = etree.Element('FieldValue')
child_3 = etree.Element('FieldIndex')
child_1.text = 'dateTime'
child_2.text = '2016-07-29T12:00:00'
child_3.text = '1'

for i in [child_1, child_2, child_3]:
    field.append(i)
a.append(field)

s = etree.tostring(tree, pretty_print=True)
print(s.decode('utf-8'))

输出

<soap:Envelope xmlns:soap="http://www...">
  <soap:Body>
    <SubmitTransaction xmlns="http://www.">
      <Authentication>
      </Authentication>
      <Transaction>
        <DataFields>
        <Field_1><FieldName>dateTime</FieldName><FieldValue>2016-07-29T12:00:00</FieldValue><FieldIndex>1</FieldIndex></Field_1></DataFields>
      </Transaction>
    </SubmitTransaction>
  </soap:Body>
</soap:Envelope>

预期

<soap:Envelope xmlns:soap="http://www...">
  <soap:Body>
    <SubmitTransaction xmlns="http://www.">
      <Authentication>
      </Authentication>
      <Transaction>
        <DataFields>
          <Field_1>
            <FieldName>dateTime</FieldName>
            <FieldValue>2016-07-29T12:00:00</FieldValue>
            <FieldIndex>1</FieldIndex>
          </Field_1>
        </DataFields>
      </Transaction>
    </SubmitTransaction>
  </soap:Body>
</soap:Envelope>

我真的不明白为什么我添加的新字段没有按预期格式化，因为如果我只打印 field，一切看起来都很好:

s = etree.tostring(root, pretty_print=True)
print(s.decode('utf-8'))

#<Field_1 xmlns="http://www." xmlns:soap="http://www...">
#  <FieldName>dateTime</FieldName>
#  <FieldValue>2016-07-29T12:00:00</FieldValue>
#  <FieldIndex>1</FieldIndex>
#</Field_1>

注意:我使用的是 python 3.4(这就是我必须 .decode('utf-8') 的原因，否则我只会得到字节文字)。

Answer 1

如果您在 a = get_data_fields() 之后添加此行，它会起作用:

a.text = None

lxml 不能总是确定哪些空格是可忽略的，因此在某些情况下需要手动删除空格。

参见 http://lxml.de/FAQ.html#why-doesn-t-the-pretty-print-option-reformat-my-xml-output :

If you want to be sure all blank text is removed from an XML document (or just more blank text than the parser does by itself), you have to use either a DTD to tell the parser which whitespace it can safely ignore, or remove the ignorable whitespace manually after parsing, e.g. by setting all tail text to None: