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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 snapshot(name, snap_name=None, desc=None, runas=None):
    '''
    Create a snapshot

    :param str name:
        Name/ID of VM to take a snapshot of

    :param str snap_name:
        Name of snapshot

    :param str desc:
        Description of snapshot

    :param str runas:
        The user that the prlctl command will be run as

    Example:

    .. code-block:: bash

        salt '*' parallels.create_snapshot macvm snap_name=macvm-original runas=macdev
        salt '*' parallels.create_snapshot macvm snap_name=macvm-updates desc='clean install with updates' runas=macdev
    '''
    # Validate VM and snapshot names
    name = salt.utils.data.decode(name)
    if snap_name:
        snap_name = salt.utils.data.decode(snap_name)

    # Construct argument list
    args = [name]
    if snap_name:
        args.extend(['--name', snap_name])
    if desc:
        args.extend(['--description', desc])

    # Execute command and return output
    return prlctl('snapshot', args, runas=runas)