Resolved: Getting errors when computing the length of list of lists

Question:

I have a list of lists. I am trying to find the indices of lists whose length is 4. Here is the code:
Alongside the correct indices, I also get the index of a list whose length is 1. Is there something wrong in my code? I have no idea why this happens.

Answer:

When you iterate over list_of_lists like so, j is the inner list, so you need to check whether len(j) == 4:

If you have better answer, please add a comment about this, thank you!