scientific-programming-exercises/exam/ex01/receive.py

import logging
from url import construct_url
from proxy import get_data_with_proxy, NoMoreProxiesException
from db_util import get_page_id

logger = logging.getLogger(__name__)

def ignore_title(title):
	ignore_starters = ["Help:"
			, "Wikipedia:"
			, "Template:"
			, "Template_talk:"
			, "Category:"
			]
	for ignore in ignore_starters:
		if(title.startswith(ignore)):
			return True
	return False

def _receive_links(title, connection):
	url = construct_url(title)

	source = get_page_id(title, connection)

	result = get_data_with_proxy(url, connection)
	# This is basically because we don't know the page ID.
	for k, page_data in result["query"]["pages"].items():
		cursor = connection.cursor()
		if(not "links" in page_data):
			destination_title = page_data["title"].replace(" ", "_")
			# avoid 1-loops
			if(destination_title == title):
				continue
			if(ignore_title(title)):
				continue
			destination = get_page_id(destination_title, connection)
			cursor.execute("INSERT INTO links(source, destination) VALUES(%s, %s)", (source, destination))
			yield destination_title

		else:
			for destination in page_data["links"]:
				if(ignore_title(title)):
					continue
				destination_title = destination["title"].replace(" ", "_")
				destination = get_page_id(destination_title, connection)
				cursor.execute("INSERT INTO links(source, destination) VALUES(%s, %s)", (source, destination))
				yield destination_title
		connection.commit()

def receive_links(title, connection):
	return list(_receive_links(title, connection))


def receive_link_graph(title, connection, depth, fetch_missing=True):
	cursor = connection.cursor()

	# Fetch the missing links.
	if(fetch_missing):
		delete_cursor = connection.cursor()
		cursor.execute('''SELECT pages.title, failed_to_fetch.depth, failed_to_fetch.page
				FROM failed_to_fetch
				LEFT JOIN pages ON pages.page_id=failed_to_fetch.page''')
		for t, d, p in cursor:
			receive_link_graph(t, connection, d, fetch_missing=False)
			delete_cursor.execute("DELETE FROM failed_to_fetch WHERE page=%s", (p,))


	if(depth < 0):
		# end of recursion
		return

	page = get_page_id(title, connection)

	cursor = connection.cursor()
	cursor.execute("SELECT COUNT(source) FROM links WHERE source=%s", (page,))
	if(cursor.fetchone()[0] != 0):
		# we fetched that title already
		return

	logger.info("fetching links for {}".format(title))

	for link in _receive_links(title, connection):
		try:
			receive_link_graph(link, connection, depth - 1)
		except NoMoreProxiesException as e:
			logger.exception("All proxies are blocked")
			# Wikipedia blocked all our proxies. 
			# Retry later, so we have to store our list that is still to fetch.

			cursor = connection.cursor() 
			failed_page = get_page_id(link, connection)
			cursor.execute("INSERT INTO failed_to_fetch(page, depth) VALUES(%s, %s)", (failed_page, depth - 1))
			connection.commit()