ElementTree XML API not matching subelement

Question

I am attempting to use the USPS API to return the status of package tracking. I have a method that returns an ElementTree.Element object built from the XML string returned from the USPS API.

This is the returned XML string.

<?xml version="1.0" encoding="UTF-8"?>
  <TrackResponse>
    <TrackInfo ID="EJ958088694US">
      <TrackSummary>The Postal Service could not locate the tracking information for your 
       request. Please verify your tracking number and try again later.</TrackSummary>
    </TrackInfo>
  </TrackResponse>

I format that into an Element object

response = xml.etree.ElementTree.fromstring(xml_str)

Now I can see in the xml string that the tag 'TrackSummary' exists and I would expect to be able to access that using ElementTree's find method.

As extra proof I can iterate over the response object and prove that the 'TrackSummary' tag exists.

for item in response.iter():
    print(item, item.text)

returns:

<Element 'TrackResponse' at 0x00000000041B4B38> None
<Element 'TrackInfo' at 0x00000000041B4AE8> None
<Element 'TrackSummary' at 0x00000000041B4B88> The Postal Service could not locate the tracking information for your request. Please verify your tracking number and try again later.

So here is the problem.

print(response.find('TrackSummary')

returns

None

Am I missing something here? Seems like I should be able to find that child element without a problem?

Answer 1

The .find() method only searches the next layer, not recursively. To search recursively, you need to use an XPath query. In XPath, the double slash // is a recursive search. Try this:

# returns a list of elements with tag TrackSummary
response.xpath('//TrackSummary')

# returns a list of the text contained in each TrackSummary tag
response.xpath('//TrackSummary/node()')

Answer 2

import xml.etree.cElementTree as ET # 15 to 20 time faster

response = ET.fromstring(str)

Xpath Syntax Selects all child elements. For example, */egg selects all grandchildren named egg.

element = response.findall('*/TrackSummary') # you will get a list
print element[0].text #fast print else iterate the list

>>> The Postal Service could not locate the tracking informationfor your request. Please verify your tracking number and try again later.