Explain sum(int(td.text) for td in soup.select('td:last-child')[1:])

Question

I came across this piece of code during solving a problem. I just cannot understand how the last line of the code before the print functions. Please explain.

import re
import urllib.request
from bs4 import BeautifulSoup

# url = 'http://py4e-data.dr-chuck.net/comments_42.html'
url = 'http://py4e-data.dr-chuck.net/comments_228869.html'

soup = BeautifulSoup(urllib.request.urlopen(url).read(), 'html.parser')
s = sum(int(td.text) for td in soup.select('td:last-child')[1:])

print(s)

Asked By: Raju Ritigya

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Source

Answer 1

This is the order of operations:

soup.select('td:last-child') is a method that returns a list of selected elements
[1:] is a slicing operation – it creates a new list that skips the first (zero’th) item in the list
for td in is a loop where the items of the list are assigned to td in turn
int(td.text) takes the "text" attribute of the object in td and then creates its integer equivalent
sum() sums those integers as they are generated

Answered By: tdelaney

Answer 2

You can break down the following assignment…

s = sum(int(td.text) for td in soup.select('td:last-child')[1:])

…into several statements:

all_td = soup.select('td:last-child') # get all last TD elements in each TR
rest_td = all_td[1:]  # skip the first TD among those
s = 0  # for accumulating a sum
for td in rest_td:
    val = int(td.text)  # parse the text in the TD as an integer
    s += val  # add that number to the running sum

Now you can step through these statements with a debugger, or add some print calls here and there, to see what’s going on.

Answered By: trincot

Explain sum(int(td.text) for td in soup.select('td:last-child')[1:])

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