Input and output

In plain English

Programs talk through output (text they print) and input (text the user types). print() writes a message to the screen. input() pauses the program and returns whatever the user typed as a string. To do math on that string you convert it with int() or float(). An f-string (a string starting with f) lets you drop values straight into a message inside curly braces.

Step by step

1. 1Ask a question with input("...") and store the answer in a variable.
2. 2Convert the string to a number with int() or float() inside try.
3. 3Print the result with an f-string so the value appears in the message.
4. 4Catch ValueError to handle non-numeric typing without crashing.

name = input("What is your name? ")
print(f"Hello, {name}!")

answer = input("How many lessons have you finished? ")
try:
    completed = int(answer)
    print(f"You are {completed} lessons in.")
except ValueError:
    print("That is not a whole number. Please try again.")

Common mistakes

• Forgetting that input() always returns a string, then trying to do math on it.
• Writing print(f...) but missing the f, so the curly braces print literally.
• Comparing a converted number to a string, like 10 == "10", which is always False.
• Letting bad input crash the program instead of catching ValueError.