feat: Add (has|iter)_children methods

This can improve performance when one just needs to know, if an item
has children.

capellambse/model/common/element.py

@@ -404,12 +404,24 @@ def _repr_html_(self) -> str:
     def get_children(self) -> MixedElementList:
         """Return all model elements that are children of this one.
 
-        The list returned from this method contains all model element
-        that are direct descendants of this element, with regard to the
-        XML hierarchy (usually referred to as "owned objects" in the
-        metamodel).
+        .... seealso::
+
+            :meth:`iter_children`
+        """
+        return MixedElementList(
+            self._model, [ele._element for ele in self.iter_children()]
+        )
+
+    def has_children(self) -> bool:
+        return next(self.iter_children(), None) is not None
+
+    def iter_children(self) -> t.Iterator[GenericElement]:
+        """Yield model elements that are children of this one.
+
+        The elements yielded from this generator are the direct
+        descendants of this element, with regard to the XML hierarchy
+        (usually referred to as "owned objects" in the metamodel).
         """
-        elements: list[etree._Element] = []
         for attr in dir(self):
             if attr.startswith("_"):
                 continue
@@ -422,10 +434,9 @@ def get_children(self) -> MixedElementList:
             ):
                 if acc.aslist is None:
                     if getattr(self, attr) is not None:
-                        elements.append(getattr(self, attr)._element)
+                        yield getattr(self, attr)
                 else:
-                    elements.extend(i._element for i in getattr(self, attr))
-        return MixedElementList(self._model, elements)
+                    yield from getattr(self, attr)
 
     if t.TYPE_CHECKING:
 
@@ -782,7 +793,7 @@ def __html__(self) -> markupsafe.Markup:
             return markupsafe.Markup("<p><em>(Empty list)</em></p>")
 
         fragments = ['<ol start="0" style="text-align: left;">']
-        for i in self:
+        for i in [i for i in self if i is not None]:
             fragments.append(f"<li>{i._short_html_()}</li>")
         fragments.append("</ol>")
         return markupsafe.Markup("".join(fragments))