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Print: Hello, World!

A program in Python is a list of lines, and each line (or statement) tells the computer to do something.

Let's start with the print statement. It tells the computer to print out a line. For example, this program:

print("Hello")

when run, the output will be:

Hello

print is a function, and the program above is calling the function with the argument "Hello". The argument is inside double quotes " because it is a line of text that can have spaces in it, called a string. Some other strings are "Goodbye", "Python rocks", and "In 2 years I will have 20,000 sheep".

If you call print with another string as argument, it will print that string instead. Here is your first problem: the box below contains a Python program that prints Goodbye, which you can run by clicking on the Run button, can you change the program to print Hello, World! instead? When you are done, try clicking Submit.

print("Goodbye")

Hello, World!

Vars: Variables

In Python, you can store a value in a variable if you want to use it later by name. For example, this program creates two variables x and y and stores in them the numbers 2 and 3:

x = 2
y = 3

You can also make Python do some calculations for you when setting a variable, and use print to see the answer:

teams = 20
players_per_team = 25
referees = 5
total_people_in_league = teams * players_per_team + referees
print(total_people_in_league)

This program's output will be 20 * 25 + 5, which is:

505

Can you modify the program below to calculate how much money you would make if you sold 13 balls at 37 dollars each and 19 shirts at 71 dollars each?

num_balls = 13
price_per_ball = 37
num_shirts = 19
price_per_shirt = 71
total_money = # CHANGE this line to calculate the right answer
print(total_money)

1830

AsgnOrder: Order

Plus2: Add two to a number

The code below defines a function plus_two(n) that is supposed to take an input number n, and return an output number that is n plus two. However, the code given below is wrong: if you call plus_two(4), for example, it returns the correct answer 6, but plus_two(5) should return 7 and this code returns 6. Can you fix it?

def plus_two(n):
    return 6  # Change this line!

print(plus_two(4))  # Expected: 6
print(plus_two(5))  # Expected: 7

tests = [(n, n + 2) for n in [-25,0,10,15,100,98765]]
for n, ans in tests:
    assert ans == plus_two(n), f'plus_two({n}) should be {ans} but was {plus_two(n)}'

Dbl: Double a number

The last problem asked you to add two to the input number. Now, write a function double(n) that takes an input number n, and returns an output number that is two times n:

def double(n):
    return 8

print(double(4))  # Expected: 8
print(double(5))  # Expected: 10

tests = [(n, 2 * n) for n in [-25,0,10,15,100,98765]]
for n, ans in tests:
    assert ans == double(n), f'double({n}) should be {ans} but was {double(n)}'

SumN: Sum from 1 to n

Write a function sum_to(n) that adds up all the numbers from 1 up to n. If you call sum_to(10), for example, it should return 55.

def sum_to(n):
    # Your code goes here

print(sum_to(10))  # Expected: 55

tests = [(n, sum(range(n+1))) for n in [0,10,15,100,98765]]
for n, ans in tests:
    assert ans == sum_to(n), f'sum_to({n}) should be {ans} but was {sum_to(n)}'

SumEven: Sum even numbers

Write a function sum_evens(n) that adds up all the even numbers from 1 up to n. If you call sum_evens(10), for example, it should return 2+4+6+8+10=30.

def sum_evens(n):
    # Your code goes here

print(sum_evens(10))  # Expected: 30

tests = [(n, sum(range(0,n+1,2))) for n in [0,10,15,100,98765]]
for n, ans in tests:
    assert ans == sum_evens(n), f'sum_evens({n}) should be {ans} but was {sum_evens(n)}'