Can someone explain me in detail how this code works regarding (Using Python to Access Web Data)

问题

Use urllib to read the HTML from the data files below, extract the href= vaues from the anchor tags, scan for a tag that is in a particular position relative to the first name in the list, follow that link and repeat the process a number of times and report the last name you find.

This is HTML link for data http://py4e-data.dr-chuck.net/known_by_Caragh.html

So I have to find the link at position 18 (the first name is 1). Follow that link. Repeat this process 7 times. The answer is the last name that you retrieve.

Can someone explain me line by line in detail how these 2 loops work("While", and "for").
So when I enter positi 18 is it extracts 18th line of href tag and then next 18th so on 7 times ? Because even if I Enter different number I'm still getting same answer. Thank you so much in advance.

Code:

import urllib.request, urllib.parse, urllib.error
from bs4 import BeautifulSoup
import ssl
n = 0
count = 0
url = input("Enter URL:")
numbers  = input("Enter count:")
position = input("Enter position:")

while n < 7:
    html = urllib.request.urlopen(url).read()
    soup = BeautifulSoup(html, 'html.parser')
    tags = soup('a')
    for tag in tags:
      count = count + 1
      if count == 18:
         url  = tag.get('href', None)
         print("Retrieving:" , url)
         count = 0
         break
n = n + 1

回答1:

Because even if I Enter different number I'm still getting same answer.

You're getting the same answer because you've hard coded that in with:

while n < 7

and

if count == 18

I think you've meant to have those as your variable/input. With that, you'll also need those inputs as an int, as currently, they get stored as as str. Also just note, I didn't want to type in the url each time, so hard coded that, but you can uncomment your input there, and then comment out the url = 'http://py4e-data.dr-chuck.net/known_by_Caragh.html'

import urllib.request, urllib.parse, urllib.error
from bs4 import BeautifulSoup
import ssl

n = 0
count = 0

url = 'http://py4e-data.dr-chuck.net/known_by_Caragh.html'
#url = input("Enter URL:")

numbers  = int(input("Enter count:"))
position = int(input("Enter position:"))

while n < numbers:    #<----- there's your variable of how many times to try
    html = urllib.request.urlopen(url).read()
    soup = BeautifulSoup(html, 'html.parser')
    tags = soup('a')
    for tag in tags:
      count = count + 1
      if count == position:  #<------- and the variable to get the position
         url  = tag.get('href', None)
         print("Retrieving:" , url)
         count = 0
         break
    n = n + 1    #<---- I fixed your indentation. The way it was previously would never get yourself out of the while loop because n will never increment.

来源：https://stackoverflow.com/questions/54900251/can-someone-explain-me-in-detail-how-this-code-works-regarding-using-python-to

标签

python

ssl

beautifulsoup

urllib