使用etree解析xml

Question

我正在尝试解析亚马逊产品广告API返回的XML响应，这就是那个XML内容。

<?xml version="1.0" ?>
    <ItemLookupResponse xmlns="http://webservices.amazon.com/AWSECommerceService/2010-11-01"> <OperationRequest>
        <HTTPHeaders>
            <Header Name="UserAgent" Value="TSN (Language=Python)"></Header>
        </HTTPHeaders>
        <RequestId>96ef9bc3-68a8-4bf3-a2c7-c98b8aeae00f</RequestId>
        <Arguments>
            <Argument Name="Operation" Value="ItemLookup"></Argument>
            <Argument Name="Service" Value="AWSECommerceService"></Argument>
            <Argument Name="Signature" Value="gjc4wRNum3YT82app1d06vMIDM7v44fOmZTP8Uh3LqE="></Argument><Argument Name="AssociateTag" Value="sneakick-20"></Argument>
            <Argument Name="Version" Value="2010-11-01"></Argument>
            <Argument Name="ItemId" Value="810056013349,810056013264"></Argument>
            <Argument Name="IdType" Value="UPC"></Argument>
            <Argument Name="AWSAccessKeyId" Value="AKIAIFMUMJLJOOINRVRA"></Argument>
            <Argument Name="Timestamp" Value="2012-01-03T21:26:39Z"></Argument>
            <Argument Name="ResponseGroup" Value="ItemIds"></Argument>
            <Argument Name="SearchIndex" Value="Apparel"></Argument>
        </Arguments>
       <RequestProcessingTime>0.0595830000000000</RequestProcessingTime>
      </OperationRequest>
      <Items>
          <Request>
              <IsValid>True</IsValid>
              <ItemLookupRequest>
                  <IdType>UPC</IdType>
                  <ItemId>810056013349</ItemId>
                  <ItemId>810056013264</ItemId>
                  <ResponseGroup>ItemIds</ResponseGroup>
                  <SearchIndex>Apparel</SearchIndex>
                  <VariationPage>All</VariationPage>
              </ItemLookupRequest>
          </Request>
          <Item>
              <ASIN>B000XR4K6U</ASIN>
          </Item>
          <Item>
              <ASIN>B000XR2UU8</ASIN>
          </Item>
       </Items>
    </ItemLookupResponse>

我只关心Items里面的Item标签，所以基本上，亚马逊返回的所有XML内容都是以字符串的形式给我的，我是这样解析的：

from xml.etree.ElementTree import fromstring

response = "xml string returned by amazon"
parsed = fromstring(response)
items = parsed[1] # This is how i get the Items element

# These were my attempts at getting the Item element
items.find('Item')
items.findall('Item')

这里的items就是指Items元素，但到目前为止没有成功，它一直返回None或空值。我是不是漏掉了什么，或者有没有其他方法可以解决这个问题呢？

Answer 1

命名空间问题。

你可以在所有项目前面加上命名空间，就像在这个问题或这个问题的第一个回答中提到的那样。一个可能更简单的解决办法是用一个小技巧来忽略命名空间，像这样：

xml_hacked_namespace = raw_xml.replace(' xmlsn=', ' xmlnamespace=')
doc = fromstring(xml_hacked_namespace)
item_list = doc.findall('.//Item')

如果你发现自己经常在处理xml，可能也会对lxml感兴趣。它速度更快，还提供了一些额外的方法，很多人觉得这些方法很实用。

Answer 2

这是一个命名空间的问题。这个代码可以正常运行：

from xml.etree import ElementTree as ET

XML = """<?xml version="1.0" ?>
    <ItemLookupResponse xmlns="http://webservices.amazon.com/AWSECommerceService/2010-11-01"> 
      <OperationRequest>
        <HTTPHeaders>
            <Header Name="UserAgent" Value="TSN (Language=Python)"></Header>
        </HTTPHeaders>
        <RequestId>96ef9bc3-68a8-4bf3-a2c7-c98b8aeae00f</RequestId>
        <Arguments>
            <Argument Name="Operation" Value="ItemLookup"></Argument>
            <Argument Name="Service" Value="AWSECommerceService"></Argument>
            <Argument Name="Signature" Value="gjc4wRNum3YT82app1d06vMIDM7v44fOmZTP8Uh3LqE="></Argument>
            <Argument Name="AssociateTag" Value="sneakick-20"></Argument>
            <Argument Name="Version" Value="2010-11-01"></Argument>
            <Argument Name="ItemId" Value="810056013349,810056013264"></Argument>
            <Argument Name="IdType" Value="UPC"></Argument>
            <Argument Name="AWSAccessKeyId" Value="AKIAIFMUMJLJOOINRVRA"></Argument>
            <Argument Name="Timestamp" Value="2012-01-03T21:26:39Z"></Argument>
            <Argument Name="ResponseGroup" Value="ItemIds"></Argument>
            <Argument Name="SearchIndex" Value="Apparel"></Argument>
        </Arguments>
       <RequestProcessingTime>0.0595830000000000</RequestProcessingTime>
      </OperationRequest>
      <Items>
          <Request>
              <IsValid>True</IsValid>
              <ItemLookupRequest>
                  <IdType>UPC</IdType>
                  <ItemId>810056013349</ItemId>
                  <ItemId>810056013264</ItemId>
                  <ResponseGroup>ItemIds</ResponseGroup>
                  <SearchIndex>Apparel</SearchIndex>
                  <VariationPage>All</VariationPage>
              </ItemLookupRequest>
          </Request>
          <Item>
              <ASIN>B000XR4K6U</ASIN>
          </Item>
          <Item>
              <ASIN>B000XR2UU8</ASIN>
          </Item>
       </Items>
    </ItemLookupResponse>"""

NS = "{http://webservices.amazon.com/AWSECommerceService/2010-11-01}"

doc = ET.fromstring(XML)
Item_elems = doc.findall(".//" + NS + "Item")  # All Item elements in document

print Item_elems

输出结果是：

[<Element '{http://webservices.amazon.com/AWSECommerceService/2010-11-01}Item' at 0xbf0c50>, 
<Element '{http://webservices.amazon.com/AWSECommerceService/2010-11-01}Item' at 0xbf0cd0>]

更接近你自己代码的变体：

NS = "{http://webservices.amazon.com/AWSECommerceService/2010-11-01}"
doc = ET.fromstring(XML)
items = doc[1]                           # Items element

first_item = items.find(NS + 'Item')     # First direct Item child
all_items =  items.findall(NS + 'Item')  # List of all direct Item children