crawl_the_internet.py

from urllib.request import urlopen
from urllib.parse import urlparse
from bs4 import BeautifulSoup
import re
import random

pages = set()

#Retrieves a list of all Internal links found on a page
def getInternalLinks(bs, includeUrl):
    includeUrl = '{}://{}'.format(urlparse(includeUrl).scheme, urlparse(includeUrl).netloc)

    internalLinks = []

    #Finds all links that begin with a "/"
    for link in bs.find_all('a', href=re.compile('^(/|.*' + includeUrl + ')')):
        if link.attrs['href'] is not None:
            if link.attrs['href'] not in internalLinks:
                if(link.attrs['href'].startswith('/')):
                    internalLinks.append(
                    includeUrl+link.attrs['href'])
                else:
                    internalLinks.append(link.attrs['href'])

    return internalLinks

#Retrieves a list of all external links found on a page
def getExternalLinks(bs, excludeUrl):
    externalLinks = []
    #Finds all links that start with "http" that do
    #not contain the current URL
    for link in bs.find_all('a',
        href=re.compile('^(http|www)((?!'+excludeUrl+').)*$')):
        if link.attrs['href'] is not None:
            if link.attrs['href'] not in externalLinks:
                externalLinks.append(link.attrs['href'])
    return externalLinks


def getRandomExternalLink(startingPage):
    html = urlopen(startingPage)
    bs = BeautifulSoup(html, 'html.parser')
    externalLinks = getExternalLinks(bs,
    urlparse(startingPage).netloc)

    if len(externalLinks) == 0:
        print('No external links, looking around the site for one')
        domain = '{}://{}'.format(urlparse(startingPage).scheme,
        urlparse(startingPage).netloc)
        internalLinks = getInternalLinks(bs, domain)
        return getRandomExternalLink(internalLinks[random.randint(0,
        len(internalLinks)-1)])
    else:
        return externalLinks[random.randint(0, len(externalLinks)-1)]


def followExternalOnly(startingSite):
    externalLink = getRandomExternalLink(startingSite)
    print('Random external link is: {}'.format(externalLink))
    followExternalOnly(externalLink)

followExternalOnly('https://docs.python.org/3/library/urllib.parse.html')