Better error message

Summary

This very small MR just adds two more verbose error messages for two mistakes that can appear during cfood development.

Please see the in-code comments for details.

Test Environment

There are unit tests.

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• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
  • How do I develop or debug the software? Assume novice developers.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

src/caoscrawler/converters/xml_converter.py

@@ -195,7 +195,10 @@ class XMLTagConverter(Converter):
 
 class XMLTextNodeConverter(Converter):
     def create_children(self, generalStore: GeneralStore, element: StructureElement):
-        raise NotImplementedError()
+        """
+        This converter does not create children.
+        """
+        return []
 
     def typecheck(self, element: StructureElement):
         """
@@ -210,6 +213,47 @@ class XMLTextNodeConverter(Converter):
         if not isinstance(element, XMLTextNode):
             raise TypeError("Element must be an instance of XMLTextNode.")
 
-        raise NotImplementedError()
+        vardict = {}
+
+        m_text = re.match(self.definition["match_text"], element.value,
+                          re.DOTALL)
+        if m_text is None:
+            return None
+        vardict.update(m_text.groupdict())
+
+        return vardict
+
+
+class XMLAttributeNodeConverter(Converter):
+    def create_children(self, generalStore: GeneralStore, element: StructureElement):
+        """
+        This converter does not create children.
+        """
+        return []
+
+    def typecheck(self, element: StructureElement):
+        """
+        Check whether the current structure element can be converted using
+        this converter.
+        """
+        return isinstance(element, XMLAttributeNode)
+
+    def match(self, element: StructureElement) -> Optional[dict]:
+        # See https://gitlab.indiscale.com/caosdb/src/caosdb-crawler/-/issues/145
+        # for a suggestion for the design of the matching algorithm.
+        if not isinstance(element, XMLAttributeNode):
+            raise TypeError("Element must be an instance of XMLAttributeNode.")
+
+        vardict = {}
 
-        return None
+        m_name = re.match(self.definition["match_name"], element.key)
+        if m_name is None:
+            return None
+        vardict.update(m_name.groupdict())
+
+        m_value = re.match(self.definition["match_value"], element.value)
+        if m_value is None:
+            return None
+        vardict.update(m_value.groupdict())
+
+        return vardict