IIIFマニフェストを元に画像をダウンロードするPythonスクリプト

n番煎じですが、備忘録として書き残します。

IIIFマニフェストを元に画像をダウンロードするスクリプトです。標準ライブラリのみで動作すると思います。
python iiif_dl.py https://iiif.example.com/path/to/manifest

GitHubにもアップロードしています。
https://github.com/adachi-a/iiif-image-downloader/

誤りやお気づきの点などありましたらぜひコメントいただけますと幸いです。

iiif_dl.py

import json
import os
import sys
import time
import random
from urllib import request, error

MAX_RETRIES = 3  # Maximum number of retries for failed downloads
RETRY_DELAY = 5  # Delay in seconds before retrying a failed download
DOWNLOAD_DELAY = (1, 3)  # Delay between 1 to 3 seconds between successful downloads

HEADERS = {
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36"
}

def download_image_from_url(url, filename):
    req = request.Request(url, headers=HEADERS)
    with request.urlopen(req) as response:
        content_length = int(response.getheader('Content-Length', '0'))
        received_data = response.read()

        if content_length != 0 and content_length != len(received_data):
            raise ValueError(f"Expected to download {content_length} bytes but received {len(received_data)} bytes.")

        with open(filename, 'wb') as file:
            file.write(received_data)

def download_with_retries(url, filename):
    for attempt in range(MAX_RETRIES):
        try:
            download_image_from_url(url, filename)
            return True
        except (error.URLError, ValueError):
            if attempt < MAX_RETRIES - 1:
                time.sleep(RETRY_DELAY)
    return False

def fetch_manifest_data(manifest_url):
    req = request.Request(manifest_url, headers=HEADERS)
    with request.urlopen(req) as response:
        return json.loads(response.read())

def extract_image_urls(data):
    return [
        image['resource']['service']['@id']
        for seq in data['sequences']
        for canvas in seq['canvases']
        for image in canvas['images']
    ]

def main(manifest_url):
    try:
        data = fetch_manifest_data(manifest_url)
        image_urls = extract_image_urls(data)
    except (error.URLError, json.JSONDecodeError):
        raise ValueError("Invalid Manifest URL or other errors.")

    total_images = len(image_urls)
    print(f'Downloading {total_images} images from {manifest_url}')

    for idx, image_url in enumerate(image_urls, start=1):
        local_filename = f"{idx:0>{len(str(total_images)) + 1}}.jpg"
        if os.path.exists(local_filename):
            continue
        complete_image_url = f"{image_url}/full/full/0/default.jpg"
        if download_with_retries(complete_image_url, local_filename):
            print(f"Downloaded {local_filename} ({idx}/{total_images})")
            time.sleep(random.uniform(*DOWNLOAD_DELAY))

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Please provide the manifest URL as an argument.")
        sys.exit(1)
    manifest_url = sys.argv[1]
    main(manifest_url)