lxml errors out with TypeError: Invalid input object: list

Question

I am trying to parse a xml file with a name called sample.xml and the contents are as below.

<?xml version="1.0" encoding="UTF-8"?><gudid xmlns="http://www.fda.gov/cdrh/gudid" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0" xsi:schemaLocation="http://www.fda.gov/cdrh/gudid gudid.xsd">
<device xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.fda.gov/cdrh/gudid">
  <publicDeviceRecordKey>7c36b446-020c-44ab-9ce7-a85387467e0f</publicDeviceRecordKey>
  <publicVersionStatus>New</publicVersionStatus>
  <deviceRecordStatus>Published</deviceRecordStatus>
  <identifiers>
    <identifier>
      <deviceId>M930756120810</deviceId>
      <deviceIdType>Primary</deviceIdType>
      <deviceIdIssuingAgency>HIBCC</deviceIdIssuingAgency>
      <containsDINumber xsi:nil="true"></containsDINumber>
      <pkgQuantity xsi:nil="true"></pkgQuantity>
      <pkgDiscontinueDate xsi:nil="true"></pkgDiscontinueDate>
      <pkgStatus xsi:nil="true"></pkgStatus>
      <pkgType xsi:nil="true"></pkgType>
    </identifier>
  </identifiers>
  <brandName>Life Instruments</brandName>
  <gmdnTerms>
    <gmdn>
      <gmdnPTName>Orthopaedic knife</gmdnPTName>
      <gmdnPTDefinition>A hand-held manual surgical instrument designed for cutting/shaping bone during an orthopaedic surgical intervention. It is typically a heavy, one-piece instrument with a sharp, single-edged, strong cutting blade at the distal end available in various shapes and sizes, with a handle at the proximal end. It is normally made of high-grade stainless steel. This is a reusable device.</gmdnPTDefinition>
    </gmdn>
  </gmdnTerms>
  <productCodes>
    <fdaProductCode>
      <productCode>LXH</productCode>
      <productCodeName>Orthopedic Manual Surgical Instrument</productCodeName>
    </fdaProductCode>
  </productCodes>
  <deviceSizes/>
  <environmentalConditions/>
</device>
</gudid>

And i am using the below code to parse this xml file.

from lxml import etree

file = "sample.xml"

root = etree.parse(file).xpath(
    "x:device", namespaces={"x": "http://www.fda.gov/cdrh/gudid"}
)

for event, element in etree.iterwalk(root, events=("start", "end")):
    if event == "start":
        print(event, etree.QName(element).localname, element.text)
    if event == "end":
        element.clear()

However this line

for event, element in etree.iterwalk(root, events=("start", "end")):

errors out with an error like

TypeError: Invalid input object: list

I am unable to see where I am wrong here ?

Luke Woodward · Accepted Answer · 2022-03-12 17:09:14Z

1

The .xpath(...) method returns a list of elements, but you seem to be assuming it returns a single element. Check that the list isn't empty and then use the first element out of this list:

devices = etree.parse(file).xpath(
    "x:device", namespaces={"x": "http://www.fda.gov/cdrh/gudid"}
)

if not devices:
    raise ValueError("No devices found")

device = devices[0]
for event, element in etree.iterwalk(device, events=("start", "end")):
    # rest of loop omitted...

Note also that I've changed the name of the variable from root to device, as it's not the root of your XML document: the <gudid> element is.

answered Mar 12, 2022 at 17:09

Luke Woodward

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