'ResNet constructor.
Args:
is_training: if build training or inference model.
data_format: the data_format used during computation.
one of \'channels_first\' or \'channels_last\'.'

def __init__(self, is_training, data_format):

    self._is_training = is_training
    assert (data_format in ('channels_first', 'channels_last'))
    self._data_format = data_format
