Loop Enumerate

• Reminder: We can refer to specific elements of a list using an index
  • Begin counting at 0
  • my_list[1] is second item on the list.
• Indexes can be variables:
  • my_list[x]
• Three ways to iterate over a list:

for value in lst:
    print(value)

for index in range(0, len(lst)):
    print(f"{index:03d}: {lst[index]}")

for value, index in lst.enumerate():
    print(f"{index:03d}: {value}")

• The basic foreach loop is useful when we need the values only.
• range and enumerate are useful when we also need the index.
• Switch to In-Class 11

Transforming Sequences

• In-Class 12 first_last. (Just modify existing list.)
• Build a new list.
  • Show cost_with_tax
  • In-Class 12 double_all
  • show corresponding list comprehension
• Conditionally apply rule
• Conditionally add values to the new list
  • Select positive numbers
• Concatenate vs append
• Subsequences/slice
• Don’t mutate a list as you iterate through it.