def append(self, head: CodePlan) -> None:
"""Append function of list object is overridden in order to add a check for the CodePlan
:param head:
"""
if isinstance(head, CodePlan):
head.check_contents()
super(TabHead, self).append(head)
elif isinstance(head, TabHead):
if self.is_subhead:
raise TypeError("Nested TabHeads only for 1 level allowed!")
else:
head.is_subhead = True
super(TabHead, self).append(head)
else:
raise TypeError("Wrong object added to TabHead ({}). Only CodePlan or TabHead allowed!".format(type(head)))
