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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def list_vdirs(site, app=_DEFAULT_APP):
    '''
    Get all configured IIS virtual directories for the specified site, or for
    the combination of site and application.

    Args:
        site (str): The IIS site name.
        app (str): The IIS application.

    Returns:
        dict: A dictionary of the virtual directory names and properties.

    CLI Example:

    .. code-block:: bash

        salt '*' win_iis.list_vdirs site
    '''
    ret = dict()

    ps_cmd = ['Get-WebVirtualDirectory',
              '-Site', r"'{0}'".format(site),
              '-Application', r"'{0}'".format(app),
              '|', "Select-Object PhysicalPath, @{ Name = 'name';",
              r"Expression = { $_.path.Split('/')[-1] } }"]

    cmd_ret = _srvmgr(cmd=ps_cmd, return_json=True)

    try:
        items = salt.utils.json.loads(cmd_ret['stdout'], strict=False)
    except ValueError:
        raise CommandExecutionError('Unable to parse return data as Json.')

    for item in items:
        ret[item['name']] = {'sourcepath': item['physicalPath']}

    if not ret:
        log.warning('No vdirs found in output: %s', cmd_ret)

    return ret