code: def format_version(version, build_number=None, build_tag=BUILD_TAG):
      
      formatted_version = ".".join(map(str, version))
  
      if build_number is not None:
          return "{formatted_version}-{build_tag}-{build_number}".format(**locals())
      
      return formatted_version
docs: Format a version string for use in packaging.
      
      >>> format_version([0,3,5])
      '0.3.5'
      >>> format_version([8, 8, 9], 23676)
      '8.8.9-jenkins-23676'
      >>> format_version([8, 8, 9], 23676, 'koekjes')
      '8.8.9-koekjes-23676'