code: def install_vendored(cls, prefix, root=None, expose=None):
      
      from pex import vendor
  
      root = cls._abs_root(root)
      vendored_path_items = [spec.relpath for spec in vendor.iter_vendor_specs()]
  
      installed = list(cls._iter_installed_vendor_importers(prefix, root, vendored_path_items))
      assert len(installed) <= 1, (
        'Unexpected extra importers installed for vendored code:\n\t{}'
          .format('\n\t'.join(map(str, installed)))
      )
      if installed:
        vendor_importer = installed[0]
      else:
        # Install all vendored code for pex internal access to it through the vendor import `prefix`.
        vendor_importer = cls.install(uninstallable=True,
                                      prefix=prefix,
                                      path_items=vendored_path_items,
                                      root=root)
  
      if expose:
        # But only expose the bits needed.
        exposed_paths = []
        for path in cls.expose(expose, root):
          sys.path.insert(0, path)
          exposed_paths.append(os.path.relpath(path, root))
  
        vendor_importer._expose(exposed_paths)
docs: Install an importer for all vendored code with the given import prefix.
  
      All distributions listed in ``expose`` will also be made available for import in direct,
      un-prefixed form.
  
      :param str prefix: The import prefix the installed importer will be responsible for.
      :param str root: The root path of the distribution containing the vendored code. NB: This is the
                       the path to the pex code, which serves as the root under which code is vendored
                       at ``pex/vendor/_vendored``.
      :param expose: Optional names of distributions to expose for direct, un-prefixed import.
      :type expose: list of str
      :raise: :class:`ValueError` if any distributions to expose cannot be found.