Lists, Modules, and Functions Exercises

This week we are just going to work on exercises to help reinforce what we've learn about modules, list comprehensions, and functions in Python.

Here's a starting exercise we'll go over together as a warm-up:

Warm-up Exercise: Write a function stringify that takes a list l and returns a list that contains the string form of each element in l.

In [1]:
# solution 1 (C-like, not-preferred but works)
def stringify(l):
    new_l = []
    for i in range(len(l)):
        new_l.append(str(l[i]))
    return new_l

# solution 2 (Python-like, better)
def stringify(l):
    new_l = []
    for elem in l:
        new_l.append(str(elem))
    return new_l

# solution 3 (Python-like with list comprehensions, best)
def stringify(l):
    new_l = [str(elem) for elem in l]
    return new_l

stringify([1, 2, 3, 4])
Out[1]:
['1', '2', '3', '4']

Exercise 1: Write a function sum_list that takes in a list l of numbers and returns its sum. (There is a sum command built-in to Python that does exactly this, but please don't use it for this exercise.)

In [2]:
def sum_list(l):
    total = 0
    for num in l:
        total += num
    return total

sum_list([1, 2, 3, 4, 5])
Out[2]:
15

Exercise 2: Write a function sum_even that takes an (even) integer n and returns the sum of every even integer between 1 and n. (Hint: use sum or sum_list above and a list comprehension.)

In [3]:
def sum_even(n):
    return sum_list(2*num for num in range(n+1))

sum_even(4)
Out[3]:
20

Exercise 3: Write a function find_even that takes in a list l of integers and returns a new list that contains only the even values of this list (in the same order).

In [4]:
def find_even(l):
    return [num for num in l if num % 2 == 0]

find_even([1, 2, 3, 4, 5, 6, 7, 8])
Out[4]:
[2, 4, 6, 8]

Exercise 4: Write a function number_to_list that takes an integer n and returns a new list that contains all the (base-10) digits of n in order.

In [5]:
# solution 1
def number_to_list(n):
    l = []
    while n > 10:
        l.insert(0,n % 10)
        n = n // 10
    return l
        
# solution 2
def number_to_list(n):
    return [int(d) for d in str(n)]

number_to_list(1234)
Out[5]:
[1, 2, 3, 4]

Exercise 5: Write a function is_subset that takes a list l1 and a list l2 and returns True if every element of l1 is a subset of l2. Don't worry about ordering or duplicate elements.

In [6]:
def is_subset(l1, l2):
    for elem in l1:
        if elem not in l2:
            return False
    return True

is_subset([1, 2, 3], [1, 2, 3, 4])
Out[6]:
True

Exercise 6: Write a function random_element that takes a list l and returns a random element of the list. Return each item with equal probability.

In [7]:
import random

# solution 1
def random_element(l):
    return l[random.randint(0, len(l))]

# solution 2 (if you happened to already know about random.choice or you looked it up)
def random_element(l):
    return random.choice(l)

random_element([1, 2, 3, 4, 5])
Out[7]:
2

Exericse 7: Write a function is_Tuesday that takes no arguments and prints "Happy Tuesday!" if the current day is Tuesday and "I wish it were Tuesday..." otherwise.
(Hint 1: You will need to use a module we haven't covered yet. See if you can figure it out by searching it yourself!)
(Hint 2 below this)

.

.

.

.

.

.

.

.

.

.

.

(Hint 2: Try searching "Python day of week")

In [8]:
import datetime

def is_Tuesday():
    if datetime.datetime.today().weekday() == 1:
        print("Happy Tuesday!")
    else:
        print("I wish it were Tuesday...")
        
is_Tuesday()

I wish it were Tuesday...