Lists

• Ordered collection of “stuff”
• Similar to what’s called an ‘array’ in other languages.
  • Although “stuff” doesn’t all have to be the same type.
  • [1, 'a', 3.14159] is a valid list.
• An example of a container in Python.
• is mutable (can be changed)
  • strings are not mutable.
• len(lst) returns the number of items on the list.
• How to swap the values in two variables?
• Swap first and last elements of the list (in-class 9)

Useful list operations / methods

• Create list from “iterable” things
  • list("abc")
  • list(range(5, 10))
• Avoid using list as a variable name.
• Merge lists together:
  • [1, 2, 3] + ['a', 'b', 'c']
• Grab a sublist:
  • lst = ['a', 'b', 'c', 'd', 'e', 'f'] then lst[2:5]
• Remove element from a list:
  • del lst[3]
• Append an item:
  • x = [1, 2, 3] then x.append(4)
  • Notice that [1, 2, 3] + 4 doesn’t work to add single item.
• Insert an item at a specific location
  • lst.insert(3, 'q')
• Review other useful methods in zyBook 8.2 and 8.3

Index of out of bounds

• Show what causes index out of bounds errors

Multi-dimensional lists

• You can nest lists
  • [['George', 'Washington'], ['John', 'Adams'], ['Thomas', 'Jefferson']]

Modifying lists in loops.

• Double all the values in a list

  lst = [1, 3, 9, 17, 44, 21, 36, 14]
  for index, item in enumerate(lst):
  lst[index] = item *2
  print(lst)
  

• Return a new list that is double the old (without modifying the input). (in-Class 9)
• List comprehension
  • [i * 2 for i in lst]
  • [i.lower() for in words]

  • [int(i) for i in inp.split()] (One line of input with many numbers)

    my_list = [[5, 10, 15], [2, 3, 16], [100]]
    sum_list = [sum(row) for row in my_list]
    print(sum_list)
    

• Slices
  • lst[2:5]
  • lst[-1]
  • Notice the difference between lst[0] and lst[0:1]
• Build a new array that is the reverse of a given array. (in-class 9)
• Reverse an array ‘in place’ (in-class 9)

Tuples

• Tuples are essentially immutable lists.

  t = ('a', 'b', 'c')
  t[0]
  t[0] = 7
  print(t)
  

• Useful for binding items together as a single conceptual object:
  • (2010, 12, 1)
  • Using a tuple would have given us a means for returning a date from a function.
  • go back and change the tomorrow function.
• Notice that using date[0] and date[1] can be a bit ambiguous.

• Named Tuples address this:

  Date = namedtuple('Date', ['year', 'month', 'day'])
  today = Date(2023, 9, 27)
  

• The first parameter is the name that is displayed when printed.
• Named tuples are immutable. (You can’t change them, you need to create a new one.)
• Update tomorrow to use named tuple.cd