Download all available audio books from ICE portal

iceportal.py

"""Download all available audio books from DB ICE Portal."""

import json
import os
import urllib.parse
import urllib.request

BASE = 'http://iceportal.de/api1/rs/'


def load_json(url: str, *, verbose: bool = True):
    if verbose:
        print(url)
    with urllib.request.urlopen(url) as f:
        doc = json.load(f)
    return doc


def get_page(href: str, *,
             base: str = urllib.parse.urljoin(BASE, 'page/')):
    url = urllib.parse.urljoin(base, href.lstrip('/'))
    return load_json(url)


def retrieve(source, target, *,
             base: str = urllib.parse.urljoin(BASE, 'audiobooks/path/')) -> None:
    sheet = urllib.parse.urljoin(base, source.lstrip('/'))
    path = load_json(sheet)['path']
    url = urllib.parse.urljoin(base, path)
    urllib.request.urlretrieve(url, filename=target)


audiobooks = get_page('hoerbuecher')

for group in audiobooks['teaserGroups']:
    for item in group['items']:
        print('', item['title'], sep='\n')
        page = get_page(item['navigation']['href'])

        dirname = page['title']
        # fix invalid
        dirname = dirname.replace('.', '_')
        for remove_char in ('"', '?', '&', '/', '|'):
            dirname = dirname.replace(remove_char, '')
        dirname, _, _ = dirname.partition(':')

        if not os.path.exists(dirname):
            os.makedirs(dirname)

        for file in page['files']:
            url = file['path']
            target = os.path.join(dirname,
                                  '{:d} - {}'.format(file['serialNumber'],
                                                     url.rpartition('/')[2]))
            if not os.path.exists(target):
                retrieve(url, target)

Hi! i used this script yesterday, it works for quite a while.
But then i saw the behaviour that a file was downloaded, it's size was shrinked to zero, redownloaded, shrinked to zero, redownloaded, .... . It was more or less an endless loop until the wifi connection itself got lost.
Then i debugged and saw that this behaviour was in the line urllib.request.urlretrieve(url, filename=target) in the retrieve-function.

Did someone else saw this behaviour and/or has an idea how to stop that?
Could it be that the urlretrieve got a redirect while it's loading, does a redownload, got a redirect, does a redownload and so on?
Is there a parameter for this function which would trigger to ignore such redirects/redownloads, or an other internal function which does more or less the same?
I would be happy if this urlretrieve would throw an expection/returns with an error code if this happens, so script could catch that and download the remaining files.