Lists: basic-level questions

If you need help reviewing Lists, take a look at these resources:

• Albert's and Robert's slides

Each question has a "Toggle Solution" button -- click it to reveal that question's solution.

What would Python print?

Question 1

>>> L = [1, 2, 3, 4]
>>> L[0]
______1
>>> L[100]
______IndexError
>>> L[-1]
______4
>>> L[2] = 100
>>> L
______[1, 2, 100, 4]

Question 2

>>> L = [1, 2, 3, 4]
>>> L[1:3]
______[2, 3]
>>> L[:2]
______[1, 2]
>>> L[1:]
______[2, 3, 4]
>>> L[:]
______[1, 2, 3, 4]
>>> L[0:3:2]
______[1, 3]
>>> L[::-1]
______[4, 3, 2, 1]

Question 3

>>> L = [1, 2, 3, 4]
>>> [1, 2] + [3, 4]
______[1, 2, 3, 4]
>>> [1, 2] * 2
______[1, 2, 1, 2]
>>> L.append(5)
>>> L
______[1, 2, 3, 4, 5]
>>> L.extend([6, 7])
>>> L
______[1, 2, 3, 4, 5, 6, 7]
>>> L.index(5)
______4
>>> L.remove(3)
>>> L
______[1, 2, 4, 5, 6, 7]
>>> L.pop()
______7
>>> L
______[1, 2, 4, 5, 6]

Code-Writing questions

Question 4

Implement a function reverse that takes a list as an argument and reverses the list. You should mutate the original list, without creating any new lists. Do NOT return anything.

def reverse(L):
    """Reverses L in place (i.e. doesn't create new lists).

    >>> L = [1, 2, 3, 4]
    >>> reverse(L)
    >>> L
    [4, 3, 2, 1]
    """
    "*** YOUR CODE HERE ***"

def reverse(L):
    for i in range(len(L)//2):
        L[i], L[-i-1] = L[-i-1], L[i]

Question 5

Implement a function map_mut that takes a list as an argument and maps a function f onto each element of the list. You should mutate the original lists, without creating any new lists. Do NOT return anything.

def map_mut(f, L):
    """Mutatively maps f onto each element in L.

    >>> L = [1, 2, 3, 4]
    >>> map_mut(lambda x: x**2, L)
    >>> L
    [1, 4, 9, 16]
    """
    "*** YOUR CODE HERE ***"

def map_mut(f, L):
    for i in range(len(L)):
        L[i] = f(L[i])