How should I capture multiple similar exceptions i…

For example, I am parsing an xml file element, and all 4 elements are required. My code this like this with minidom library:

id = pattern.getElementsByTagName("id")[0].firstChild.data
name = pattern.getElementsByTagName("name")[0].firstChild.data
trigger = pattern.getElementsByTagName("trigger")[0].firstChild.data
test = pattern.getElementsByTagName("test")[0].firstChild.data

If the xml document lack any of the 4 tags, I want to throw an IndexError exception. Should I use 4 try … except blocks to capture each element exception, or I should just capture all the 4 similar exceptions in one big block? The benefit of capturing individual errors is that I can print out more explicit error message regarding the lack of a specific xml element, but it looks verbose. Is there a good practice here?

try:
   id = pattern.getElementsByTagName("id")[0].firstChild.data
except IndexError:
   raise IndexError('id must exists in the xml file!')
try:
   name = pattern.getElementsByTagName("name")[0].firstChild.data
except IndexError:
   raise IndexError('name must exists in the xml file!')
try:
       test = pattern.getElementsByTagName("test")[0].firstChild.data
    except IndexError:
       raise IndexError('test must exists in the xml file!')
try:
       trigger = pattern.getElementsByTagName("trigger")[0].firstChild.data
    except IndexError:
       raise IndexError('trigger must exists in the xml file!')

try:
  id = pattern.getElementsByTagName("id")[0].firstChild.data
  name = pattern.getElementsByTagName("name")[0].firstChild.data
  trigger = pattern.getElementsByTagName("trigger")[0].firstChild.data
  test = pattern.getElementsByTagName("test")[0].firstChild.data
except IndexError:
  raise IndexError('id, name, trigger and test must exist in the xml file!')

Which one is better or both are not great?

Answer

Consider using a loop over the field names and packing the results into a dict instead!

results = {}
for field_name in ("id", "name", "trigger", "test"):
    try:
        results[field_name] = xml.getElementsByTagName(field_name)[0].firstChild.data
    except IndexError as ex:
        raise IndexError(f"failed to read '{field_name}' from xml {repr(ex)}")

How should I capture multiple similar exceptions in such a case?

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Answer