simple python exercises using the Python interpreter

Learn to use the Python interpreter to run Python code.

1. Open a terminal
2. Type python3 or python
3. Type print("Hello, World!")
4. Type x = 5
5. Type x
6. Type x + 5
7. Type x
8. Type x = x + 10
9. Type x
10. Type def println(s): print(s)
11. Type println("your name here!")

Let's save this to a file. Exit the Python interpreter with exit() or Ctrl-D.

Create a file called hello_world.py:

print("Hello, World!")
x = 5
print(x)
print(x + 5)
print(x)
x = x + 10
print(x)

def println(s):
    print(s)

println("your name here!")

Run it with: python3 hello_world.py

In the steps below, you will be using the Python interpreter to run Python code.

Start training your brain by TYPING the code into the Python interpreter. DO NOT COPY AND PASTE.

CopyPasta is the enemy of learning. It's cheating yourself. And at this point, it's cheating in this course.

Start the Python interpreter and type the following code:

Let's use a simple while loop to print out the numbers from 1 to 10.

i = 1
while i <= 10:
    print(i)
    i += 1

Now TYPE it into the Python interpreter. Notice how Python uses indentation instead of braces.

A function in Python is a block of code that performs a specific task. You use functions so you don't have to write the same code over and over again. (Programmers like to be lazy and efficient that way.)

Let's create a simple function to print out the numbers from 1 to 10.

def print_numbers():
    i = 1
    while i <= 10:
        print(i)
        i += 1

Now TYPE it into the Python interpreter. and call the function by typing print_numbers() and then pressing Enter.

Let's use a simple function to print out the numbers from 1 to n.

def print_numbers(n):
    i = 1
    while i <= n:
        print(i)
        i += 1

Now TYPE it into the Python interpreter. and call the function by typing print_numbers(5) and then pressing Enter. and then print_numbers(10) and then pressing Enter. and then print_numbers(20) and then pressing Enter.

Let's use a simple function to return the sum of the numbers from 1 to n.

def sum_numbers(n):
    i = 1
    total = 0
    while i <= n:
        total = total + i
        i += 1
    return total

Now TYPE it into the Python interpreter. and call the function by typing sum_numbers(5) and then pressing Enter. and then sum_numbers(11) and then pressing Enter. and then sum_numbers(23) and then pressing Enter. and then sum_numbers(5683) and then pressing Enter. and then sum_numbers(106839) and then pressing Enter.

Let's use a simple function to return the sum of the numbers from 1 to n.

def sum_numbers(n):
    total = 0
    for i in range(1, n + 1):
        total = total + i
    return total

Now TYPE it into the Python interpreter. and call the function by typing sum_numbers(5) and then pressing Enter. and then sum_numbers(10) and then pressing Enter. and then sum_numbers(20) and then pressing Enter. and then sum_numbers(106839) and then pressing Enter.

Let's use a simple function to return the sum of the numbers from 1 to n.

def sum_numbers(n):
    total = 0
    for i in range(1, n + 1):
        total = total + i
    return total

def sum_numbers_to_10():
    return sum_numbers(10)

Now TYPE it into the Python interpreter. and call the function by typing sum_numbers_to_10() and then pressing Enter.

Exit the Python interpreter and create a file called sum_numbers.py:

def sum_numbers(n):
    total = 0
    for i in range(1, n + 1):
        total = total + i
    return total

def sum_numbers_to_10():
    return sum_numbers(10)

def sum_numbers_to_13():
    return sum_numbers(13)

if __name__ == "__main__":
    print(sum_numbers_to_10())
    print(sum_numbers_to_13())

Run it with: python3 sum_numbers.py

Write a function that takes parameters and returns a value.

def add_two_numbers(x, y):
    return 0  # fix this

Now TYPE it into the Python interpreter. and call the function by typing add_two_numbers(5, 10) and then pressing Enter. Notice how the answer is wrong. Fix the function and run it again.

Now create 3 functions that take two parameters and return a math operation of the two numbers.

1. divide divide_two_numbers(x, y)
2. multiply multiply_two_numbers(x, y)
3. subtract subtract_two_numbers(x, y)

Let's do some functions with if statements.

Write a function that takes a parameter and returns a value.

def is_even(x):
    return 0  # fix this

Now TYPE it into the Python interpreter.

and call the function by typing is_even(5) and then pressing Enter.

Notice how the answer is wrong. Fix the function and then run it again. (what might be wrong with the function?) maybe if the number is even, return 1, otherwise return 0.

But, what if we want to return a boolean instead of an int?

Write a function that takes a parameter and returns a boolean.

def is_even(x):
    return False  # fix this

Now TYPE it into the Python interpreter.

and call the function by typing is_even(5) and then pressing Enter. So... what's wrong with the function? maybe if the number is even, return True, otherwise return False.

Write a function that takes a parameter and returns a boolean.

def is_odd(x):
    return False  # fix this

Now TYPE it into the Python interpreter. and call the function by typing is_odd(5) and then pressing Enter.

How can we tell if a number is odd or even? The most common way is to use the modulo operator %.

See how it works:

x = 5
y = 2
x % y

What does it return? What does it mean?

now write a while loop that prints out the numbers from 1 to 10 and prints out the modulo of each number with 2.

i = 1
while i <= 10:
    print(f"{i} % 2 = {i % 2}")
    i += 1

Now TYPE it into the Python interpreter.

Hmm. It appears that the % (mod or modulo) operator returns 0 if the number is even and 1 if the number is odd.

How can we use that in is_even and is_odd functions?

You'll need an if statement to check if the number is even or odd.

def is_even(x):
    return x % 2 == 0

And now you write the is_odd function. Remember != means "not equal to".

You could also use == and make the 0 a 1, right?

Write a function that prints "odd" or "even" for the numbers from 1 to 10.

def print_odd_even():
    i = 1
    while i <= 10:
        if is_even(i):
            print(f"{i} is even")
        else:
            print(f"{i} is odd")
        i += 1

see the else part? what if you remove it? (puzzle over it in your mind. c'mon experiment!)

Now TYPE it into the Python interpreter.

You've done a lot of work. You've learned a lot about the Python interpreter and Python functions. Make sure you save it all to github.

git add .
git commit -m "done with Python interpreter and PythonSmall"
git push

Now, switch to VARS.md and learn about variables in Python.