使用 LXML xml 设置没有值的属性

Question

我要：

<div data-a>

但是 LXML API 似乎只给我这个：

<div data-a=''>

如何获得无价值的属性？

LXML 将空白值和空值表示为空白字符串，这很烦人。

设置 None 值没有帮助。

In [19]: from lxml.html import fromstring, tostring

In [20]: b = fromstring('<body class="meow" data-a="haha" data-b data-x="">text-fef27e87389e466fb99b5421629323f6</body>')

In [21]: b.attrib
Out[21]: {'data-a': 'haha', 'data-x': '', 'data-b': '', 'class': 'meow'}

In [22]: b = fromstring('<body class="meow" data-a="haha" data-b data-x="">text-fef27e87389e466fb99b5421629323f6</body>')

In [23]: b.attrib
Out[23]: {'data-a': 'haha', 'data-x': '', 'data-b': '', 'class': 'meow'}

In [24]: b.attrib['data-y'] = None
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-24-1f55133e3dc4> in <module>()
----> 1 b.attrib['data-y'] = None

/usr/lib/python2.7/dist-packages/lxml/etree.so in lxml.etree._Attrib.__setitem__ (src/lxml/lxml.etree.c:58775)()

/usr/lib/python2.7/dist-packages/lxml/etree.so in lxml.etree._setAttributeValue (src/lxml/lxml.etree.c:19025)()

/usr/lib/python2.7/dist-packages/lxml/etree.so in lxml.etree._utf8 (src/lxml/lxml.etree.c:26460)()

TypeError: Argument must be bytes or unicode, got 'NoneType'


tag.attrib['data-a'] = None
TypeError: Argument must be bytes or unicode, got 'NoneType'

Answer 1

恕我直言，lxml 正在展示预期的行为。没有值的属性会导致格式不正确 XML，而体面的 XML 解析器不会生成格式不正确的 XML :

关于 XML 中没有值的属性：Is an xml attribute without a value, valid?
关于术语 格式正确 XML : Is there a difference between 'valid xml' and 'well formed xml'?

Answer 2

看起来您实际上是在尝试操纵 HTML 而不是 XML。如果是这样，则使用 lxml.html 而不是 lxml.etree。

您正在尝试设置一个 "boolean attribute"，不要与 "boolean value" 混淆（参见 boolean-attributes）。正如另一个答案中已经指出的那样，布尔属性语法不是 allowed.e

但是，由于您试图操纵 HTML 似乎很明显，因此您创建了一个带有 HTML 元素而不是 XML 元素的布尔属性。

import unittest

import lxml.html

class HtmlBooleanAttribute(unittest.TestCase):

    def test_booleanAttribute(self):

        # !!! BE SURE TO CREATE AN ****HTML**** ELEMENT !!!
        div = lxml.html.Element('div')

        # Set a boolean attribute; omitting the value or providing None will
        # create a boolean attribute.
        div.set('data-a')
        div.set('data-b', None)

        # Setting the value to an empty will not give you a boolean attribute
        div.set('data-c', '')

        # Set a normal attribute for comparison
        div.set('class','big red')

        print
        print lxml.html.tostring(div)
        print

        # Note that 'data-a' will be a zero-length string
        print 'data-a = ', div.get('data-a')
        print 'type(data-a) = ', type(div.get('data-a'))
        print 'len(data-a) = ', len(div.get('data-a'))

        print

        print 'data-c = ', div.get('data-c')
        print 'type(data-c) = ', type(div.get('data-c'))
        print 'len(data-c) = ', len(div.get('data-c'))






if __name__ == "__main__":
    #import sys;sys.argv = ['', 'Test.testName']
    unittest.main()

输出

<div data-a data-b data-c="" class="big red"></div>

data-a =  
type(data-a) =  <type 'str'>
len(data-a) =  0

data-c =  
type(data-c) =  <type 'str'>
len(data-c) =  0
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

请注意，data-a 和 data-b 都是零长度字符串，但它们的打印方式不同。

使用 LXML xml 设置没有值的属性

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