system-design-primer/solutions/system_design/web_crawler/web_crawler_snippets.py

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2017-03-05 12:06:58 +07:00
# -*- coding: utf-8 -*-
class PagesDataStore(object):
def __init__(self, db);
self.db = db
...
def add_link_to_crawl(self, url):
"""Add the given link to `links_to_crawl`."""
...
def remove_link_to_crawl(self, url):
"""Remove the given link from `links_to_crawl`."""
...
def reduce_priority_link_to_crawl(self, url)
"""Reduce the priority of a link in `links_to_crawl` to avoid cycles."""
...
def extract_max_priority_page(self):
"""Return the highest priority link in `links_to_crawl`."""
...
def insert_crawled_link(self, url, signature):
"""Add the given link to `crawled_links`."""
...
def crawled_similar(self, signature):
"""Determine if we've already crawled a page matching the given signature"""
...
class Page(object):
def __init__(self, url, contents, child_urls):
self.url = url
self.contents = contents
self.child_urls = child_urls
self.signature = self.create_signature()
def create_signature(self):
# Create signature based on url and contents
...
class Crawler(object):
def __init__(self, pages, data_store, reverse_index_queue, doc_index_queue):
self.pages = pages
self.data_store = data_store
self.reverse_index_queue = reverse_index_queue
self.doc_index_queue = doc_index_queue
def crawl_page(self, page):
for url in page.child_urls:
self.data_store.add_link_to_crawl(url)
self.reverse_index_queue.generate(page)
self.doc_index_queue.generate(page)
self.data_store.remove_link_to_crawl(page.url)
self.data_store.insert_crawled_link(page.url, page.signature)
def crawl(self):
while True:
page = self.data_store.extract_max_priority_page()
if page is None:
break
if self.data_store.crawled_similar(page.signature):
self.data_store.reduce_priority_link_to_crawl(page.url)
else:
self.crawl_page(page)
page = self.data_store.extract_max_priority_page()