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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 AddLabels(self, labels):
 """Adds labels to the event tag. Args: labels (list[str]):
 labels. Raises: ValueError: if a label is malformed. """

    for label in labels:
      if not self._VALID_LABEL_REGEX.match(label):
        raise ValueError((
            'Unsupported label: "{0:s}". A label must only consist of '
            'alphanumeric characters or underscores.').format(label))

    for label in labels:
      if label not in self.labels:
        self.labels.append(label)