Input and output

Estimated Time: 30 minutes

Key ideas

• Show output with print()
• Get data from the user with input()

Printing Output

Websites and apps you have used in the past have a whole screen full of text and buttons. Eventually, you’ll learn to build those kinds of programs, but we’re starting with the basics: programs that work with text.

print shows some output to the Console:

print("Hello, world")

You’ve written code like this from your first “Hello, World” program. When you run it, the output shows up.

In Replit, output shows in the ‘Console’ tab. On early computers, there was only a text console. On the earliest computers, there wasn’t a screen at all. Instead, the output was printed out on paper. The output now shows up in the Console in our web browser, but we still call the function print.

print("We can print any string we want")
x = ("If the string is in a variable, we can print the variable")
print(x) # If the string is in a variable, we can print the variable

Getting Input from the User

You've already used the input() function in earlier challenges to get the name from the user.

When Python sees input:

• It prints out the arguments to input, similar to print.
• It pauses to wait for the user to type something in
• It waits for the user to press Enter
• When the user presses Enter, input gives the program the text that the user typed in

We can design lots of text-based interactions using input. A calculator, a search engine, a quiz, a chatbot - all of these and more can be designed to use text input and output.

Converting Inputs

The input() function returns a string. If you want a number, need to convert the data type using int or float.

response = input("How old are you?")
age = int(response)

It’s common to see the input and the conversion all at once, like this:

age = int(input("How old are you?"))

Converting to a float is similar:

soda_price = float(input("How much does a soda cost?"))

int("3.5") # ValueError: invalid literal for int() with base 10: '3.5'

Practice: Assigning and printing user input

Experimenting With Print

print()
print
print("Hello", "world")

What happens when there’s nothing between the parentheses? Or if you leave off the parentheses? Or if you put more than one thing between the parentheses?

Sometimes, the best way to find things out about how Python works is to try it out.

Experiment with print to find out what it does in different situations

https://replit.com/@kibocurriculum/Explore-With-Print

Print with multiple arguments

The print() function can take more than one argument. It can have more than one thing inside the parentheses (...)

However, you must separate arguments by commas.

name = "Emmy"
print("Hello" name) # SyntaxError: invalid syntax (because there's no comma)
print("Hello", name) # Hello Emmy

Example: Input and Output

Here's the code for the exercise:

1. first_num = int(input("enter first number: "))
2. second_num = int(input("enter second number: "))
3.
4. total = first_num + second_num
5.
6. print("the sum is: ", total)

In plain English, here is what the code does:

• line 1: Ask the user for an input. Convert the input to an integer, and store it in a variable named first_num
• line 2: Ask the user for another input. Convert the input to an integer, and store it in a variable named second_num
• line 4: Add first_num and second_num and put the result in a third variable named total
• line 6: Print out the string "the sum is" and the value of the variable named total

Practice: Add three numbers

first_num = int(input("enter first number: "))
second_num = int(input("enter second number: "))
third_num = int(input("enter third number: "))

# change the line below
total = first_num + second_num + third_num

# edit the text that will show up
print("the sum of the three numbers is: ", total)