def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
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