from this link : https://github.com/bentrevett/pytorch-sentiment-analysis/blob/master/4%20-%20Convolutional%20Sentiment%20Analysis.ipynb 16
You will see they use this code for generate iterator.
import torch
from torchtext import data
from torchtext import datasets
import random

SEED = 1234

torch.manual_seed(SEED)
torch.cuda.manual_seed(SEED)

TEXT = data.Field(tokenize='spacy')
LABEL = data.LabelField(tensor_type=torch.FloatTensor)
train, test = datasets.IMDB.splits(TEXT, LABEL)
train, valid = train.split(random_state=random.seed(SEED))
BATCH_SIZE = 64

train_iterator, valid_iterator, test_iterator = data.BucketIterator.splits(
    (train, valid, test), 
    batch_size=BATCH_SIZE, 
    sort_key=lambda x: len(x.text), 
    repeat=False)

Is it possible to create my iterator with the torchtext function