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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def append(self, child):
 """Add a child section or keyword"""

        if not (isinstance(child, CP2KSection) or isinstance(child, CP2KKeyword)):
            raise TypeError("The child must be a CP2KSection or a CP2KKeyword, got: %s." % child)
        l = self.__index.setdefault(child.name, [])
        l.append(child)
        self.__order.append(child)