code: def get_minimum_span(low, high, span):
      
      if is_number(low) and low == high:
          if isinstance(low, np.datetime64):
              span = span * np.timedelta64(1, 's')
          low, high = low-span, high+span
      return low, high
docs: If lower and high values are equal ensures they are separated by
      the defined span.