在ElementTree中使用XPath

Question

我的XML文件如下所示:

<?xml version="1.0"?>
<ItemSearchResponse xmlns="http://webservices.amazon.com/AWSECommerceService/2008-08-19">
  <Items>
    <Item>
      <ItemAttributes>
        <ListPrice>
          <Amount>2260</Amount>
        </ListPrice>
      </ItemAttributes>
      <Offers>
        <Offer>
          <OfferListing>
            <Price>
              <Amount>1853</Amount>
            </Price>
          </OfferListing>
        </Offer>
      </Offers>
    </Item>
  </Items>
</ItemSearchResponse>

我想做的就是提取ListPrice.

这是我正在使用的代码:

>> from elementtree import ElementTree as ET
>> fp = open("output.xml","r")
>> element = ET.parse(fp).getroot()
>> e = element.findall('ItemSearchResponse/Items/Item/ItemAttributes/ListPrice/Amount')
>> for i in e:
>>    print i.text
>>
>> e
>>

绝对没有输出.我也试过了

>> e = element.findall('Items/Item/ItemAttributes/ListPrice/Amount')

没有不同.

我究竟做错了什么？

Answer 1

你有两个问题.

1)element只包含根元素,而不是递归地包含整个文档.它的类型为Element而不是ElementTree.

2)如果将命名空间保留在XML中,则搜索字符串需要使用命名空间.

解决问题#1:

你需要改变:

element = ET.parse(fp).getroot()

至:

element = ET.parse(fp)

解决问题#2:

您可以从XML文档中取出xmlns,使其如下所示:

<?xml version="1.0"?>
<ItemSearchResponse>
  <Items>
    <Item>
      <ItemAttributes>
        <ListPrice>
          <Amount>2260</Amount>
        </ListPrice>
      </ItemAttributes>
      <Offers>
        <Offer>
          <OfferListing>
            <Price>
              <Amount>1853</Amount>
            </Price>
          </OfferListing>
        </Offer>
      </Offers>
    </Item>
  </Items>
</ItemSearchResponse>

使用此文档,您可以使用以下搜索字符串:

e = element.findall('Items/Item/ItemAttributes/ListPrice/Amount')

完整代码:

from elementtree import ElementTree as ET
fp = open("output.xml","r")
element = ET.parse(fp)
e = element.findall('Items/Item/ItemAttributes/ListPrice/Amount')
for i in e:
  print i.text

对问题#2的替代解决方法:

否则,您需要在srearch字符串中为每个元素指定xmlns.

完整代码:

from elementtree import ElementTree as ET
fp = open("output.xml","r")
element = ET.parse(fp)

namespace = "{http://webservices.amazon.com/AWSECommerceService/2008-08-19}"
e = element.findall('{0}Items/{0}Item/{0}ItemAttributes/{0}ListPrice/{0}Amount'.format(namespace))
for i in e:
    print i.text

两个印刷品:

2260

Answer 2

from xml.etree import ElementTree as ET
tree = ET.parse("output.xml")
namespace = tree.getroot().tag[1:].split("}")[0]
amount = tree.find(".//{%s}Amount" % namespace).text

另外,请考虑使用lxml.它的速度更快.

from lxml import ElementTree as ET

Answer 3

元素树使用名称空间,因此xml中的所有元素都具有{ http://weweservices.amazon.com/AWSECommerceService/2008-08-19 }之类的名称

因此,使搜索包括命名空间,例如

search = '{http://webservices.amazon.com/AWSECommerceService/2008-08-19}Items/{http://webservices.amazon.com/AWSECommerceService/2008-08-19}Item/{http://webservices.amazon.com/AWSECommerceService/2008-08-19}ItemAttributes/{http://webservices.amazon.com/AWSECommerceService/2008-08-19}ListPrice/{http://webservices.amazon.com/AWSECommerceService/2008-08-19}Amount'
element.findall( search )

给出对应于2260的元素

Answer 4

我最终从原始xml中剥离出xmlns,如下所示:

def strip_ns(xml_string):
    return re.sub('xmlns="[^"]+"', '', xml_string)

显然对此非常小心,但它对我来说效果很好.