code: def find_missing_dependencies(self, requirement):
          
          known_dependencies = self.find_known_dependencies(requirement)
          if known_dependencies:
              installed_packages = self.find_installed_packages()
              logger.debug("Checking for missing dependencies of %s ..", requirement.name)
              missing_dependencies = sorted(set(known_dependencies).difference(installed_packages))
              if missing_dependencies:
                  logger.debug("Found %s: %s",
                               pluralize(len(missing_dependencies), "missing dependency", "missing dependencies"),
                               concatenate(missing_dependencies))
              else:
                  logger.info("All known dependencies are already installed.")
              return missing_dependencies
docs: Find missing dependencies of a Python package.
  
          :param requirement: A :class:`.Requirement` object.
          :returns: A list of strings with system package names.