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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 vgextend(vgname, devices):
    '''
    Add physical volumes to an LVM volume group

    CLI Examples:

    .. code-block:: bash

        salt mymachine lvm.vgextend my_vg /dev/sdb1,/dev/sdb2
        salt mymachine lvm.vgextend my_vg /dev/sdb1
    '''
    if not vgname or not devices:
        return 'Error: vgname and device(s) are both required'
    if isinstance(devices, six.string_types):
        devices = devices.split(',')

    cmd = ['vgextend', vgname]
    for device in devices:
        cmd.append(device)
    out = __salt__['cmd.run'](cmd, python_shell=False).splitlines()
    vgdata = {'Output from vgextend': out[0].strip()}
    return vgdata