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Recap
Iterating over a list
Modifying lists
Working with multiple lists
Congratulations
16. Summary

Instruction

Well done! It's time to wrap things up. Let's summarize what we've learned before we take the quiz.

  1. Use a for loop to iterate over a list. You may need one or more variables defined before the loop.
    numbers = [2, 45, 32, 1]
    sum = 0
    for number in numbers:
      sum += number
  2. You can usethe enumerate() function with a for loop.
    first_sum = 0
    second_sum = 0
    for i, number in enumerate(numbers):
      if i < 2:
        first_sum += number
      else:
        second_sum += number
    
  3. If you want to update list elements, iterate over the indexes.
    for i in range(len(numbers)):
      numbers[i] = ...
  4. To change the element order, iterate over the indexes.
    for i in range(0, len(numbers), 2):
      numbers[i], numbers[i+1] = numbers[i+1], numbers[i]
    
  5. To safely delete list elements, iterate over a copy of the list using [:].
    for number in numbers[:]:
      numbers.remove(number)
  6. When creating a new list based on an existing one, you will typically need an empty list before the loop with an append() function inside it.
    neg_numbers = []
    for number in numbers:
      neg_numbers.append(-1 * number)
  7. To compare two same-sized lists element by element, iterate over the indexes of either list.
    numbers1 = [4, 98, 23, 43]
    numbers2 = [2, 45, 32, 1]
    for i in range (len(numbers1)):
      if numbers1[i] > numbers2[i]:
        ...
  8. When comparing two lists with different sizes, watch out for IndexErrors: iterate over the shorter list or check if the current index is within the bounds.
    numbers1 = [2, 45]
    numbers2 = [2, 45, 32, 1]
    • iterate over the shorter list
      for i in numbers1:
        ...
    • check the index inside
      for i in numbers2:
        if i < len(numbers1):
          ...
  9. When merging sorted lists or searching for common elements, you will typically need a while loop and two variables to store the current list indexes.
    i, j = 0, 0
    while i < len(list1) and j < len(list2):
      if ...: i += 1
      if ...: j += 1

Quite a lot! All right, it's time for a short quiz.

Exercise

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