code: def cvss_base_v2_value(cls, cvss_base_vector):
          
          if not cvss_base_vector:
              return None
  
          _av, _ac, _au, _c, _i, _a = cls._parse_cvss_base_vector(
              cvss_base_vector)
  
          _impact = 10.41 * (1 - (1 - cvss_v2_metrics['C'].get(_c)) *
                             (1 - cvss_v2_metrics['I'].get(_i)) *
                             (1 - cvss_v2_metrics['A'].get(_a)))
  
          _exploitability = (20 * cvss_v2_metrics['AV'].get(_av) *
                             cvss_v2_metrics['AC'].get(_ac) *
                             cvss_v2_metrics['Au'].get(_au))
  
          f_impact = 0 if _impact == 0 else 1.176
  
          cvss_base = ((0.6 * _impact) + (0.4 * _exploitability) - 1.5) * f_impact
  
          return round(cvss_base, 1)
docs: Calculate the cvss base score from a cvss base vector
          for cvss version 2.
          Arguments:
              cvss_base_vector (str) Cvss base vector v2.
  
          Return the calculated score