获取复杂元素的属性使用lxm

Question

我有一个简单的XML文件，如下所示：

    <brandName type="http://example.com/codes/bmw#" abbrev="BMW" value="BMW" />BMW</brandName>
      <maxspeed>
        <value>250</value>
        <unit type="http://example.com/codes/units#" value="miles per hour" abbrev="mph" />
      </maxspeed>

我想用lxml解析它并得到它的值： 对于brandName，它只需要：

^{pr2}$

如果我想了解它的缩写属性。在

    'brand_name'  : m.findtext(NS+'brandName').attrib['abbrev']

使用maxspeed，我可以通过以下方法获得maxspeed的值：

    'maxspeed_value'                  : m.findtext(NS+'maxspeed/value'),

或者：

    'maxspeed_value'                  : m.find(NS+'maxspeed/value').text,

现在，我想得到单位的属性里面，我尝试了很多不同的方法，但我失败了。大多数情况下的错误是：

    'NoneType' object has no attribute 'attrib'

以下是我尝试过但失败的几种方法：

    'maxspeed_unit'                  : m.find(NS+'maxspeed/value').attrib['abbrev'],
    'maxspeed_unit'                  : (m.find(NS+'maxspeed/value'))get('abbrev'),

你能告诉我为什么它不起作用吗？ 非常感谢你！在

更新XML:

    <Car xmlns="http://example.com/vocab/xml/cars#">
     <dateStarted>2011-02-05</dateStarted>
     <dateSold>2011-02-13</dateSold>
    <name type="http://example.com/codes/bmw#" abbrev="X6" value="BMW X6" >BMW X6</name>
    <brandName type="http://example.com/codes/bmw#" abbrev="BMW" value="BMW" />BMW</brandName>
      <maxspeed>
        <value>250</value>
        <unit type="http://example.com/codes/units#" value="miles per hour" abbrev="mph" />
      </maxspeed>
      <route type="http://example.com/codes/routes#" abbrev="HW" value="Highway" >Highway</route>
      <power>
        <value>180</value>
        <unit type="http://example.com/codes/units#" value="powerhorse" abbrev="ph" />
      </power>
      <frequency type="http://example.com/codes/frequency#" value="daily" >Daily</frequency>  
    </Car>

Answer 1

import lxml.etree as ET
content='''
<Car xmlns="http://example.com/vocab/xml/cars#">
 <brandName type="http://example.com/codes/bmw#" abbrev="BMW" value="BMW" >BMW</brandName>
   <maxspeed>
     <value>250</value>
     <unit type="http://example.com/codes/units#" value="miles per hour" abbrev="mph" />
   </maxspeed>
 </Car>
'''

doc=ET.fromstring(content)
NS = 'http://example.com/vocab/xml/cars#'
# print(ET.tostring(doc,pretty_print=True))
for x in doc.xpath('//ns:maxspeed/ns:unit/@abbrev',namespaces={'ns': NS}):
    print(x)

收益率

^{pr2}$

Answer 2

lxml元素上的.find方法将只搜索该元素的直接子子级。例如，在这个xml中：

<root>
    <brandName type="http://example.com/codes/bmw#" abbrev="BMW" value="BMW">BMW</brandName>
    <maxspeed>
        <value>250</value>
        <unit type="http://example.com/codes/units#" value="miles per hour" abbrev="mph" />
    </maxspeed>
</root>

您可以使用根元素.find方法来定位brandname元素或maxspeed元素，但是搜索不会在这些内部元素中遍历。在

例如，你可以这样做：

^{pr2}$

从这个返回的元素可以访问属性。在

如果要搜索XML文档中的所有元素，可以使用.iter（）方法。对于前面的例子，您可以说：

for element in root.iter(tag='unit'):
    print element #This would print all the unit elements in the document.

编辑：下面是一个使用您提供的xml的全功能小示例：

import lxml.etree
from StringIO import StringIO

def ns_join(element, tag, namespace=None):
    '''Joins the namespace and tag together, and
    returns the fully qualified name.
    @param element - The lxml.etree._Element you're searching
    @param tag - The tag you're joining
    @param namespace - (optional) The Namespace shortname default is None'''

    return '{%s}%s' % (element.nsmap[namespace], tag)

def parse_car(element):
    '''Parse a car element, This will return a dictionary containing
    brand_name, maxspeed_value, and maxspeed_unit'''

    maxspeed = element.find(ns_join(element,'maxspeed'))
    return { 
        'brand_name' : element.findtext(ns_join(element,'brandName')), 
        'maxspeed_value' : maxspeed.findtext(ns_join(maxspeed,'value')), 
        'maxspeed_unit' : maxspeed.find(ns_join(maxspeed, 'unit')).attrib['abbrev']
        }

#Create the StringIO object to feed to the parser.
XML = StringIO('''
<Reports>
    <Car xmlns="http://example.com/vocab/xml/cars#">
        <dateStarted>2011-02-05</dateStarted>
        <dateSold>2011-02-13</dateSold>
        <name type="http://example.com/codes/bmw#" abbrev="X6" value="BMW X6" >BMW X6</name>
        <brandName type="http://example.com/codes/bmw#" abbrev="BMW" value="BMW" >BMW</brandName>
        <maxspeed>
            <value>250</value>
            <unit type="http://example.com/codes/units#" value="miles per hour" abbrev="mph" />
        </maxspeed>
        <route type="http://example.com/codes/routes#" abbrev="HW" value="Highway" >Highway</route>
        <power>
            <value>180</value>
            <unit type="http://example.com/codes/units#" value="powerhorse" abbrev="ph" />
        </power>
        <frequency type="http://example.com/codes/frequency#" value="daily" >Daily</frequency>  
    </Car>
</Reports>
''')

#Get the root element object of the xml
car_root_element = lxml.etree.parse(XML).getroot()

# For each 'Car' tag in the root element,
# we want to parse it and save the list as cars
cars = [ parse_car(element) 
    for element in car_root_element.iter() if element.tag.endswith('Car')]

print cars

希望有帮助。在