Pixiv downloader without login, requires BeautifulSoup4 and requests to work properly

get_pixiv.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import re
import bs4
import sys
import requests

if len(sys.argv) != 2:
    print >> sys.stderr, 'usage: ./get_pixiv.py <illustration_url>'
    exit(1)

url = None
html = requests.get(sys.argv[1]).text
html = bs4.BeautifulSoup(html, 'html.parser')

for div in html.find_all('div'):
    if div.has_attr('class'):
        if len(div['class']) == 1 and div['class'][0] == 'img-container':
            for img in div.find_all('img'):
                if img.has_attr('src') and img['src'].startswith('https://i.pximg.net/'):
                    url = img['src']
                    break

if url is None:
    print >> sys.stderr, 'Sorry, but no valid illustration URLs found.'
    exit(1)

p = re.compile(r'.+/(\d{4})/(\d{2})/(\d{2})/(\d{2})/(\d{2})/(\d{2})/(\d+)_(\w+)_.*\..*$')
match = p.match(url)

if not match or len(match.groups()) != 8:
    print >> sys.stderr, 'Sorry, but no valid illustration URLs found.'
    exit(1)

for ext in ['jpg', 'png']:
    fn = '%s_%s.%s' % (match.groups()[-2:] + (ext,))
    url = 'https://i.pximg.net/img-original/img/%s/%s/%s/%s/%s/%s/%s_%s.%s' % (match.groups() + (ext,))
    resp = requests.get(url, headers = {
        'Host'            : 'i.pximg.net',
        'User-Agent'      : "Mozilla/5.0 (Windows NT 6.1; rv:32.0) Gecko/20100101 Firefox/32.0",
        'Accept'          : '*/*',
        'Accept-Encoding' : 'gzip, deflate, br',
        'Accept-Language' : 'zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3',
        'Referer'         : sys.argv[1],
        'Connection'      : 'keep-alive',
        'Cache-Control'   : 'no-cache',
    })

    if resp.status_code == 200:
        break

if resp.status_code != 200:
    print >> sys.stderr, 'Sorry, but server returned %d' % resp.status_code
    exit(1)

print 'File Name:', fn
print 'Real Image URL:', url

with open(fn, 'wb') as f:
    for chunk in resp.iter_content(16384):
        f.write(chunk)