sys.argv list index out of range error

Question

I am trying to run this script that grabs rss feeds on the environment "Thonny" but I just keep receiving this error of "IndexError: List index out of range"

Traceback (most recent call last):
File "C:\Users\uri\rssfeedfour.py", line 11, in <module>
url = sys.argv[1]
IndexError: list index out of range

How do I resolve this to keep from getting this error over and over again. Im not sure how to solve this as I am a beginner. Do I need to define it, if so how? or could I take it out and go a different direction? Here is the code.

import feedparser
import time
from subprocess import check_output
import sys

#feed_name = 'TRIBUNE'
#url = 'http://chicagotribune.feedsportal.com/c/34253/f/622872/index.rss'

feed_name = sys.argv[1]
url = sys.argv[2]

db = 'http://feeds.feedburner.com/TheHackersNews'
limit = 12 * 3600 * 1000

current_time_millis = lambda: int(round(time.time() * 1000))
current_timestamp = current_time_millis()

def post_is_in_db(title):
    with open(db, 'r') as database:
        for line in database:
            if title in line:
                return True
    return False


def post_is_in_db_with_old_timestamp(title):
    with open(db, 'r') as database:
        for line in database:
            if title in line:
                ts_as_string = line.split('|', 1)[1]
                ts = long(ts_as_string)
                if current_timestamp - ts > limit:
                    return True
    return False

#
# get the feed data from the url
#
feed = feedparser.parse(url)

#
# figure out which posts to print
#
posts_to_print = []
posts_to_skip = []

for post in feed.entries:
    # if post is already in the database, skip it
    # TODO check the time
    title = post.title
    if post_is_in_db_with_old_timestamp(title):
        posts_to_skip.append(title)
    else:
        posts_to_print.append(title)

#
# add all the posts we're going to print to the database with the current timestamp
# (but only if they're not already in there)
#
f = open(db, 'a')
for title in posts_to_print:
    if not post_is_in_db(title):
        f.write(title + "|" + str(current_timestamp) + "\n")
f.close

#
# output all of the new posts
#
count = 1
blockcount = 1
for title in posts_to_print:
    if count % 5 == 1:
        print("\n" + time.strftime("%a, %b %d %I:%M %p") + '  ((( ' + feed_name + ' - ' + str(blockcount) + ' )))')
        print("-----------------------------------------\n")
        blockcount += 1
    print(title + "\n")
    count += 1

Answer 1

sys.argv is a list in Python, which contains the command-line arguments passed to the script. sys.argv[0] contains the name of the script, sys.argv[1] contains the first argument and so on.

To prevent this error, you need to give command line arguments when starting the script. For example, you can start this script without any errors by

python rssfeedfour.py TRIBUNE http://chicagotribune.feedsportal.com/c/34253/f/622872/index.rss

You can also modify the script so that it works using the default arguments if you don't provide any command line arguments.

try:
    feed_name = sys.argv[1]
except IndexError:
    feed_name = 'TRIBUNE'

try: 
    url = sys.argv[2]
except IndexError:
    url = 'http://chicagotribune.feedsportal.com/c/34253/f/622872/index.rss'

You can learn more about handling errors here .

Although it is much more convenient to use argparse library.