code: def installation_refused(self, requirement, missing_dependencies, reason):
          
          msg = "Missing %s (%s) required by Python package %s (%s) but %s!"
          raise DependencyInstallationRefused(
              msg % (pluralize(len(missing_dependencies), "system package", "system packages"),
                     concatenate(missing_dependencies),
                     requirement.name,
                     requirement.version,
                     reason)
          )
docs: Raise :exc:`.DependencyInstallationRefused` with a user friendly message.
  
          :param requirement: A :class:`.Requirement` object.
          :param missing_dependencies: A list of strings with missing dependencies.
          :param reason: The reason why installation was refused (a string).