code: def repository_url_part(distro):
      
      if distro.normalized_release.int_major >= 6:
          if distro.normalized_name == 'redhat':
              return 'rhel' + distro.normalized_release.major
          if distro.normalized_name in ['centos', 'scientific', 'oracle', 'virtuozzo']:
              return 'el' + distro.normalized_release.major
  
      return 'el6'
docs: Historically everything CentOS, RHEL, and Scientific has been mapped to
      `el6` urls, but as we are adding repositories for `rhel`, the URLs should
      map correctly to, say, `rhel6` or `rhel7`.
  
      This function looks into the `distro` object and determines the right url
      part for the given distro, falling back to `el6` when all else fails.
  
      Specifically to work around the issue of CentOS vs RHEL::
  
          >>> import platform
          >>> platform.linux_distribution()
          ('Red Hat Enterprise Linux Server', '7.0', 'Maipo')