How to use the mmcv.is_list_of function in mmcv

def run(self, data_loaders, workflow, max_epochs, **kwargs):
        """Start running.

        Args:
            data_loaders (list[:obj:`DataLoader`]): Dataloaders for training
                and validation.
            workflow (list[tuple]): A list of (phase, epochs) to specify the
                running order and epochs. E.g, [('train', 2), ('val', 1)] means
                running 2 epochs for training and 1 epoch for validation,
                iteratively.
            max_epochs (int): Total training epochs.
        """
        assert isinstance(data_loaders, list)
        assert mmcv.is_list_of(workflow, tuple)
        assert len(data_loaders) == len(workflow)

        self._max_epochs = max_epochs
        work_dir = self.work_dir if self.work_dir is not None else 'NONE'
        self.logger.info('Start running, host: %s, work_dir: %s',
                         get_host_info(), work_dir)
        self.logger.info('workflow: %s, max: %d epochs', workflow, max_epochs)
        self.call_hook('before_run')

        while self.epoch < max_epochs:
            for i, flow in enumerate(workflow):
                mode, epochs = flow
                if isinstance(mode, str):  # self.train()
                    if not hasattr(self, mode):
                        raise ValueError(
                            'runner has no method named "{}" to run an epoch'.

def random_select(img_scales):
        assert mmcv.is_list_of(img_scales, tuple)
        scale_idx = np.random.randint(len(img_scales))
        img_scale = img_scales[scale_idx]
        return img_scale, scale_idx

def random_sample(img_scales):
        assert mmcv.is_list_of(img_scales, tuple) and len(img_scales) == 2
        img_scale_long = [max(s) for s in img_scales]
        img_scale_short = [min(s) for s in img_scales]
        long_edge = np.random.randint(
            min(img_scale_long),
            max(img_scale_long) + 1)
        short_edge = np.random.randint(
            min(img_scale_short),
            max(img_scale_short) + 1)
        img_scale = (long_edge, short_edge)
        return img_scale, None

def __init__(self,
                 img_scale=None,
                 multiscale_mode='range',
                 ratio_range=None,
                 keep_ratio=True):
        if img_scale is None:
            self.img_scale = None
        else:
            if isinstance(img_scale, list):
                self.img_scale = img_scale
            else:
                self.img_scale = [img_scale]
            assert mmcv.is_list_of(self.img_scale, tuple)

        if ratio_range is not None:
            # mode 1: given a scale and a range of image ratio
            assert len(self.img_scale) == 1
        else:
            # mode 2: given multiple scales or a range of scales
            assert multiscale_mode in ['value', 'range']

        self.multiscale_mode = multiscale_mode
        self.ratio_range = ratio_range
        self.keep_ratio = keep_ratio

def __init__(self,
                 img_scale=None,
                 multiscale_mode='range',
                 ratio_range=None,
                 keep_ratio=True):
        if img_scale is None:
            self.img_scale = None
        else:
            if isinstance(img_scale, list):
                self.img_scale = img_scale
            else:
                self.img_scale = [img_scale]
            assert mmcv.is_list_of(self.img_scale, tuple)

        if ratio_range is not None:
            # mode 1: given a scale and a range of image ratio
            assert len(self.img_scale) == 1
        else:
            # mode 2: given multiple scales or a range of scales
            assert multiscale_mode in ['value', 'range']

        self.multiscale_mode = multiscale_mode
        self.ratio_range = ratio_range
        self.keep_ratio = keep_ratio

def random_sample(img_scales):
        assert mmcv.is_list_of(img_scales, tuple) and len(img_scales) == 2
        img_scale_long = [max(s) for s in img_scales]
        img_scale_short = [min(s) for s in img_scales]
        long_edge = np.random.randint(
            min(img_scale_long),
            max(img_scale_long) + 1)
        short_edge = np.random.randint(
            min(img_scale_short),
            max(img_scale_short) + 1)
        img_scale = (long_edge, short_edge)
        return img_scale, None

def random_select(img_scales):
        assert mmcv.is_list_of(img_scales, tuple)
        scale_idx = np.random.randint(len(img_scales))
        img_scale = img_scales[scale_idx]
        return img_scale, scale_idx

def random_sample(img_scales):
        assert mmcv.is_list_of(img_scales, tuple) and len(img_scales) == 2
        img_scale_long = [max(s) for s in img_scales]
        img_scale_short = [min(s) for s in img_scales]
        long_edge = np.random.randint(
            min(img_scale_long),
            max(img_scale_long) + 1)
        short_edge = np.random.randint(
            min(img_scale_short),
            max(img_scale_short) + 1)
        img_scale = (long_edge, short_edge)
        return img_scale, None

def run(self, data_loaders, workflow, max_epochs, **kwargs):
        """Start running.

        Args:
            data_loaders (list[:obj:`DataLoader`]): Dataloaders for training
                and validation.
            workflow (list[tuple]): A list of (phase, epochs) to specify the
                running order and epochs. E.g, [('train', 2), ('val', 1)] means
                running 2 epochs for training and 1 epoch for validation,
                iteratively.
            max_epochs (int): Total training epochs.
        """
        assert isinstance(data_loaders, list)
        assert mmcv.is_list_of(workflow, tuple)
        assert len(data_loaders) == len(workflow)

        self._max_epochs = max_epochs
        work_dir = self.work_dir if self.work_dir is not None else 'NONE'
        self.logger.info('Start running, host: %s, work_dir: %s',
                         get_host_info(), work_dir)
        self.logger.info('workflow: %s, max: %d epochs', workflow, max_epochs)
        self.call_hook('before_run')

        while self.epoch < max_epochs:
            for i, flow in enumerate(workflow):
                mode, epochs = flow
                if isinstance(mode, str):  # self.train()
                    if not hasattr(self, mode):
                        raise ValueError(
                            'runner has no method named "{}" to run an epoch'.

def random_select(img_scales):
        assert mmcv.is_list_of(img_scales, tuple)
        scale_idx = np.random.randint(len(img_scales))
        img_scale = img_scales[scale_idx]
        return img_scale, scale_idx