Delete item in a list using a for-loop

Question

I have an array with subjects and every subject has connected time. I want to compare every subjects in the list. If there are two of the same subjects, I want to add the ti

Answer 1

Though a while loop is certainly a better choice for this, if you insist on using a for loop, one can replace the list elements-to-be-deleted with None, or any other distinguishable item, and redefine the list after the for loop. The following code removes even elements from a list of integers:

nums = [1, 1, 5, 2, 10, 4, 4, 9, 3, 9]
for i in range(len(nums)):
  # select the item that satisfies the condition
  if nums[i] % 2 == 0:
    # do_something_with_the(item)
    nums[i] = None  # Not needed anymore, so set it to None
# redefine the list and exclude the None items
nums = [item for item in nums if item is not None]
# num = [1, 1, 5, 9, 3, 9]

In the case of the question in this post:

...
for i in range(subjectlength - 1):
  for j in range(i+1, subjectlength):
    if subject[i] == subject[j]:
      #add
      time[i] += time[j]
        # set to None instead of delete
        time[j] = None
        subject[j] = None
time = [item for item in time if item is not None]
subject = [item for item in subject if item is not None]