How to use the virtualenv.make_environment_relocatable function in virtualenv

env, search_dirs=virtualenv.file_search_dirs())

  if not quiet:
    print '  Activating environment'
  # Ensure hermeticity during activation.
  os.environ.pop('PYTHONPATH', None)
  bin_dir = 'Scripts' if sys.platform.startswith('win') else 'bin'
  activate_this = os.path.join(env, bin_dir, 'activate_this.py')
  execfile(activate_this, dict(__file__=activate_this))

  if cur_deps is None:
    if not quiet:
      print '  Installing deps'
      print_deps(deps, indent=2, with_implicit=False)
    install(deps)
    virtualenv.make_environment_relocatable(env)
    with open(manifest_path, 'wb') as f:
      f.write(repr(deps) + '\n')

  # Create bin\python.bat on Windows to unify path where Python is found.
  if sys.platform.startswith('win'):
    bin_path = os.path.join(env, 'bin')
    if not os.path.isdir(bin_path):
      os.makedirs(bin_path)
    python_bat_path = os.path.join(bin_path, 'python.bat')
    if not os.path.isfile(python_bat_path):
      with open(python_bat_path, 'w') as python_bat_file:
        python_bat_file.write(PYTHON_BAT_WIN)

  if not quiet:
    print 'Done creating environment'

run_command(['{}/{}/bin/pip'.format(project_path,
                                            cfg.VIRTUAL_ENV_PATH),
                     'install',
                     '-U',
                     'pip'])

        if not os.path.exists('{}/requirements.txt'.format(project_path)):
            logger.warning('requirements.txt not found')
            return ve_path

        run_command(['{}/{}/bin/pip'.format(project_path,
                                            cfg.VIRTUAL_ENV_PATH),
                     'install',
                     '-r',
                     '{}/requirements.txt'.format(project_path)])
        virtualenv.make_environment_relocatable(ve_path)
        fixup_scripts(install_path, ve_path)
    except Exception:
        logger.exception('failed to install requirements! error message:')
        raise Exception('fail to install requirements.')
    return ve_path

fh.write(site_py)

  if not quiet:
    print '  Activating environment'
  # Ensure hermeticity during activation.
  os.environ.pop('PYTHONPATH', None)
  bin_dir = 'Scripts' if sys.platform.startswith('win') else 'bin'
  activate_this = os.path.join(env, bin_dir, 'activate_this.py')
  execfile(activate_this, dict(__file__=activate_this))

  if cur_deps is None:
    if not quiet:
      print '  Installing deps'
      print_deps(deps, indent=2, with_implicit=False)
    install(deps, cache_root)
    virtualenv.make_environment_relocatable(env)
    with open(manifest_path, 'wb') as f:
      f.write(repr(deps) + '\n')

  # Create bin\python.bat on Windows to unify path where Python is found.
  if sys.platform.startswith('win'):
    bin_path = os.path.join(env, 'bin')
    if not os.path.isdir(bin_path):
      os.makedirs(bin_path)
    python_bat_path = os.path.join(bin_path, 'python.bat')
    if not os.path.isfile(python_bat_path):
      with open(python_bat_path, 'w') as python_bat_file:
        python_bat_file.write(PYTHON_BAT_WIN)

  if not quiet:
    print 'Done creating environment'