tqdm not showing bar

tqdm needs to known how many iters will be performed (the total amount) to show a progress bar.

You can try this:

from tqdm import tqdm

train_x = range(100)
train_y = range(200)

train_iter = zip(train_x, train_y)

# Notice `train_iter` can only be iter over once, so i get `total` in this way.
total = min(len(train_x), len(train_y))

with tqdm(total=total) as pbar:
    for item in train_iter:
        # do something ...
        pbar.update(1)