114 lines
4.7 KiB
Markdown
114 lines
4.7 KiB
Markdown
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# Tornado
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[Tornado](http://www.tornadoweb.org/) is a Python web framework and asynchronous networking library, originally developed at [FriendFeed](https://en.wikipedia.org/wiki/FriendFeed). By using non-blocking network I/O, Tornado can scale to tens of thousands of open connections, making it ideal for [long polling](http://en.wikipedia.org/wiki/Push_technology#Long_polling), [WebSockets](http://en.wikipedia.org/wiki/WebSocket), and other applications that require a long-lived connection to each user.
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Tornado can be roughly divided into three major components:
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- A web framework (including [`RequestHandler`](https://www.tornadoweb.org/en/stable/web.html#tornado.web.RequestHandler "tornado.web.RequestHandler") which is subclassed to create web applications, and various supporting classes).
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- Client- and server-side implementions of HTTP ([`HTTPServer`](https://www.tornadoweb.org/en/stable/httpserver.html#tornado.httpserver.HTTPServer "tornado.httpserver.HTTPServer") and [`AsyncHTTPClient`](https://www.tornadoweb.org/en/stable/httpclient.html#tornado.httpclient.AsyncHTTPClient "tornado.httpclient.AsyncHTTPClient")).
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- An asynchronous networking library including the classes [`IOLoop`](https://www.tornadoweb.org/en/stable/ioloop.html#tornado.ioloop.IOLoop "tornado.ioloop.IOLoop") and [`IOStream`](https://www.tornadoweb.org/en/stable/iostream.html#tornado.iostream.IOStream "tornado.iostream.IOStream"), which serve as the building blocks for the HTTP components and can also be used to implement other protocols.
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The Tornado web framework and HTTP server together offer a full-stack alternative to [WSGI](http://www.python.org/dev/peps/pep-3333/). While it is possible to use the Tornado HTTP server as a container for other WSGI frameworks ([`WSGIContainer`](https://www.tornadoweb.org/en/stable/wsgi.html#tornado.wsgi.WSGIContainer "tornado.wsgi.WSGIContainer")), this combination has limitations and to take full advantage of Tornado you will need to use Tornado’s web framework and HTTP server together.
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----
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Example of concurrent web spider with ```tornado.queues```
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```
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#!/usr/bin/env python3
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import asyncio
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import time
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from datetime import timedelta
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from html.parser import HTMLParser
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from urllib.parse import urljoin, urldefrag
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from tornado import gen, httpclient, queues
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base_url = "http://www.tornadoweb.org/en/stable/"
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concurrency = 10
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async def get_links_from_url(url):
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"""Download the page at `url` and parse it for links.
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Returned links have had the fragment after `#` removed, and have been made
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absolute so, e.g. the URL 'gen.html#tornado.gen.coroutine' becomes
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'http://www.tornadoweb.org/en/stable/gen.html'.
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"""
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response = await httpclient.AsyncHTTPClient().fetch(url)
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print("fetched %s" % url)
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html = response.body.decode(errors="ignore")
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return [urljoin(url, remove_fragment(new_url)) for new_url in get_links(html)]
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def remove_fragment(url):
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pure_url, frag = urldefrag(url)
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return pure_url
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def get_links(html):
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class URLSeeker(HTMLParser):
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def __init__(self):
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HTMLParser.__init__(self)
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self.urls = []
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def handle_starttag(self, tag, attrs):
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href = dict(attrs).get("href")
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if href and tag == "a":
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self.urls.append(href)
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url_seeker = URLSeeker()
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url_seeker.feed(html)
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return url_seeker.urls
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async def main():
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q = queues.Queue()
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start = time.time()
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fetching, fetched, dead = set(), set(), set()
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async def fetch_url(current_url):
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if current_url in fetching:
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return
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print("fetching %s" % current_url)
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fetching.add(current_url)
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urls = await get_links_from_url(current_url)
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fetched.add(current_url)
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for new_url in urls:
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# Only follow links beneath the base URL
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if new_url.startswith(base_url):
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await q.put(new_url)
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async def worker():
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async for url in q:
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if url is None:
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return
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try:
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await fetch_url(url)
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except Exception as e:
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print("Exception: %s %s" % (e, url))
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dead.add(url)
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finally:
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q.task_done()
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await q.put(base_url)
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# Start workers, then wait for the work queue to be empty.
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workers = gen.multi([worker() for _ in range(concurrency)])
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await q.join(timeout=timedelta(seconds=300))
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assert fetching == (fetched | dead)
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print("Done in %d seconds, fetched %s URLs." % (time.time() - start, len(fetched)))
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print("Unable to fetch %s URLS." % len(dead))
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# Signal all the workers to exit.
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for _ in range(concurrency):
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await q.put(None)
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await workers
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if __name__ == "__main__":
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asyncio.run(main())
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```
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