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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 resize(mountpoint, size):
    '''
    Resize filesystem.

    General options:

    * **mountpoint**: Specify the BTRFS mountpoint to resize.
    * **size**: ([+/-]<newsize>[kKmMgGtTpPeE]|max) Specify the new size of the target.

    CLI Example:

    .. code-block:: bash

        salt '*' btrfs.resize /mountpoint size=+1g
        salt '*' btrfs.resize /dev/sda1 size=max
    '''

    if size == 'max':
        if not salt.utils.fsutils._is_device(mountpoint):
            raise CommandExecutionError("Mountpoint \"{0}\" should be a valid device".format(mountpoint))
        if not salt.utils.fsutils._get_mounts("btrfs").get(mountpoint):
            raise CommandExecutionError("Device \"{0}\" should be mounted".format(mountpoint))
    elif len(size) < 3 or size[0] not in '-+' \
         or size[-1] not in 'kKmMgGtTpPeE' or re.sub(r"\d", "", size[1:][:-1]):
        raise CommandExecutionError("Unknown size: \"{0}\". Expected: [+/-]<newsize>[kKmMgGtTpPeE]|max".format(size))

    out = __salt__['cmd.run_all']('btrfs filesystem resize {0} {1}'.format(size, mountpoint))
    salt.utils.fsutils._verify_run(out)

    ret = {'log': out['stdout']}
    ret.update(__salt__['btrfs.info'](mountpoint))

    return ret