How can I ignore a Specific Index? Python

Question

I am trying to parse a JSON output and if a Index has the userId of 5, I want to ignore it. The problem is that it still does not ignore it.

Here is how i read the json (works):

import json
import urllib.request

url = "https://jsonplaceholder.typicode.com/posts"
data = urllib.request.urlopen(url).read().decode()

site_info =json.loads(data)

for info in site_info:
  print(f"{}, {}, {}, {}".format(info["userId"], info["id"],
                                 info["title"], info["body"]))

Here is how I prepare a list of userIds to inspect (removal of 5 does not work):

mylist= [{"userId":1}, {"userId":2}, {"userId":3}, {"userId":4}, {"userId":5}, 
         {"userId":6}, {"userId":7}, {"userId":8}, {"userId":9}, {"userId":10}]

for i in range(len(mylist)-5, -5, -5):
    print(i)
    if mylist[i]["userId"] == 5:
        mylist.pop(i)

print (mylist)

I also need to use .pop as part of the assignment.

Patrick Artner · Accepted Answer · 2021-09-17T05:12:39.997

Your code does exactly what you told it to:

it checks the positions 5 and 0 on your mylist n
if either had a mylist[i]["userId"] == 5 something would be done
neither has mylist[i]["userId"] == 5 so it does nothing.

Beside that: NEVER change a list while iterating (unless you know how-to - you do not do it correctly).

You can remember indexes to pop and pop them seperately:

idx_to_delete = []

for idx,value in enumerate(mylist):
    if value["userId"] == 5:
        idx_to_delete.append(idx)

# reverse - because if you pop 2 and then 5 the popping of 2
# would lead to 5 now being 4 etc. if you pop the higher ones 
# first you do not have that problem.
# reversed(idx_to_delete) == idx_to_delete[::-1]
for id in reversed(idx_to_delete):
    mylist.pop(id)

To raise the quality of your question, you should

remove all the JSON stuff - you never use site_info for your actual problem so it does not belong into a minimal reproducible example
get rid of things that confuse you: range(len(mylist)-5, -5, -5) evaluates to range(10-5, -5, -5) and results in 5,0 if iterated - so replace it with for i in (5,0):. If you check mylist[5] and mylist[0] you'll see that NEITHER has a ["userId"] == 5.

Your questions code would boil down to

mylist= [{"userId":1},{"userId":2},{"userId":3},{"userId":4},{"userId":5}, 
         {"userId":6},{"userId":7},{"userId":8},{"userId":9},{"userId":10}]

for i in (5,0):
    print(i)
    if mylist[i]["userId"] == 5:
        mylist.pop(i)

print (mylist)

Why does the "userId" == 5 not get popped? List is unchanged?

If would probably be easier if you did

id_to_ignore = {5,}

mylist = [{"userId":id} for id in range(10) if id not in id_to_ignore]

# or as loop
# mylist = []
# for id in range(1,11):
#    if id in id_to_ignore: 
#        continue
#    mylist.append( {"userId":id})

How can I ignore a Specific Index? Python

1 Answers1