def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def set_categories(self, categories: List[str]):
        """Sets the categories for Confusion Matrix.

        Args:
          categories: List of strings specifying the categories.
        """
        self._categories = []
        annotation_specs = []
        for category in categories:
            annotation_spec = {'displayName': category}
            self._categories.append(category)
            annotation_specs.append(annotation_spec)

        self._values['annotationSpecs'] = annotation_specs
        self._matrix = [[0
                         for i in range(len(self._categories))]
                        for j in range(len(self._categories))]
        self._values['row'] = self._matrix