docs: def array(self):
          """ Returns :prop:intervals as a numpy array, caches
  
              -> :class:numpy.array
          """
          if self._intervals_len:
              if self._array_len != self._intervals_len:
                  if not self._array_len:
                      self._array = np.array(self.intervals) \
                          if hasattr(np, 'array') else self.intervals
                  else:
                      self._array = np.concatenate((
                          self._array, self.intervals), axis=0) \
                          if hasattr(np, 'concatenate') else \
                          (self._array + self.intervals)
                  self._array_len += len(self.intervals)
                  self.intervals = []
              return self._array
          return []