Q:

Scraping data from multiple previous dates in WSJ stocks website

I am scraping data from WSJ Biggest Gainers website. I am new to Python, so I'm sure this is simple. I just can't find a clear answer to this.
My code currently only downloads the data from one page, but I want it to go back to the previous days of data, for example, and find_all or select the data from the charts. How can I modify the URL in the code to do this? I am using Python 3.4.3 and bs4.
The nice thing is that the previous days website URLs only differ in a few numbers.
For example,
This is last Friday
http://online.wsj.com/mdc/public/page/2_3021-gainnnm-gainer-20150731.html?mod=mdc_pastcalendar
This is last Thursday
http://online.wsj.com/mdc/public/page/2_3021-gainnnm-gainer-20150730.html?mod=mdc_pastcalendar
Ideally I would like to be able to change the month, date, or year if I wish, and then loop the different page URLs to retrieve the data I wish.
Here is my code:
import requests 
from bs4 import BeautifulSoup

url = 'http://online.wsj.com/mdc/public/page/2_3021-gainnyse-gainer.html'

r = requests.get(url)           #downloads website html

soup = BeautifulSoup(r.content)         #soup calls the data

v_data = soup.select('.text') 

for symbol in v_data:
    print(symbol.text)

I just want to loop this function for the past X days. I have tried making a list of URLs to run with no luck. It is also more work to make a list of URLs, so if I could use something like %s or %d for month, year, and date, then that would be better.

A:

You can use a start date, then -= a day using timedelta passing the date to the url with str.format and strftime:
import requests
from bs4 import BeautifulSoup
from datetime import date,timedelta
start_url = "http://online.wsj.com/mdc/public/page/2_3021-gainnnm-gainer-{}.html?mod=mdc_pastcalendar"

start = date.today()
for _ in range(5):
    url = start_url.format(start.strftime("%Y%m%d"))
    start -= timedelta(days=1)
    r = requests.get(url)           #downloads website html
    soup = BeautifulSoup(r.content)         #soup calls the data
    v_data = soup.select('.text')
    for symbol in v_data:
        print(symbol.text)

Just create whatever date you want. If you want a particular start date, just create a datetime object:
import requests
from bs4 import BeautifulSoup
from datetime import datetime,timedelta
start_url = "http://online.wsj.com/mdc/public/page/2_3021-gainnnm-gainer-{}.html?mod=mdc_pastcalendar"

start = datetime(2015,07,31)
for _ in range(5):
    print("Data for {}".format(start.strftime("%b %d %Y")))
    url = start_url.format(start.strftime("%Y%m%d"))
    start -= timedelta(days=1)
    r = requests.get(url)           #downloads website html
    soup = BeautifulSoup(r.content)         #soup calls the data
    v_data = soup.select('.text')
    for symbol in v_data:
        print(symbol.text.rstrip())
    print(" ")

Output:
Data for Jul 31 2015

|
WHAT'S THIS?
|
1

MoneyGram International (MGI)
2

YRC Worldwide (YRCW)
3

Immersion (IMMR)
4

Skywest (SKYW)
5

Vital Therapies (VTL)
6

..........................

Data for Jul 30 2015

|
WHAT'S THIS?
|
1

H&E Equipment Services (HEES)
2

Senomyx (SNMX)
3

eHealth (EHTH)
4

Nutrisystem (NTRI)
5

Open Text (OTEX)
6

LivePerson (LPSN)
7

Sonus Networks (SONS)
8

FormFactor (FORM)
9

Pegasystems (PEGA)
10

Town Sports International Holdings (CLUB)
11

FARO Technologies (FARO)
12

Presbia (LENS)
13

If you only want to include weekdays and still get n days, then we need to add a little more logic.
import requests
from bs4 import BeautifulSoup
from datetime import datetime, timedelta

start_url = "http://online.wsj.com/mdc/public/page/2_3021-gainnnm-gainer-{}.html?mod=mdc_pastcalendar"

start = datetime(2015, 7, 31)

def only_weekdays_range(start, n):
    i = 0
    wk_days = {0, 1, 2, 3, 4}
    while i != n:
        while start.weekday() not in wk_days:
            start -= timedelta(days=1)
        yield start
        i += 1
        start -= timedelta(days=1)

for dte in (only_weekdays_range(start, 2)):
    print("Data for {}".format(start.strftime("%b %d %Y")))
    url = start_url.format(start.strftime("%Y%m%d"))
    print(url)
    r = requests.get(url)  #downloads website html
    soup = BeautifulSoup(r.content)  #soup calls the data
    v_data = soup.select('.text')
    for symbol in v_data:
        print(symbol.text.rstrip())
    print(" ")

The only_weekdays_range will get n days from our start date excluding weekends. You can do so by: print(list(only_weekdays_range(datetime(2015, 7, 26), 2))). We get [datetime.datetime(2015, 7, 24, 0, 0), datetime.datetime(2015, 7, 23, 0, 0)], which is friday the 24th and thursday the 23rd, because our start day is Sunday the 26th
If you want to also exclude holidays, then that is quite a bit more work. Another approach would only be to decrement n when you get data returned from v_data, but that could lead to infinite loops for various reasons.

