input(), int(), float() and validation. Learn through short examples, practical tasks and targeted questions.
input() always returns text, even if the user types digits. Programs that need to compare or calculate numerical values must convert that string using int() or float(). Test a whole number, a decimal and non-numeric input to discover when conversion can fail.
Watch out: Do not assume the user will enter a valid number: int("hello") raises a ValueError unless the program handles it.
input(), int(), float() and validation. Study the code and predict what it does before running it. Change a value or string and observe how the output changes.
name = input("Your name: ")
year = int(input("Birth year: "))
print("Hello", name, "— in 2030 you will be", 2030 - year)Ask for a distance in kilometres, convert it to miles using 0.621371 and display a rounded answer.
Plan your inputs, processing and outputs. Write the code in Mu, IDLE or PyCharm; test at least three cases.
km = float(input("Kilometres: "))
miles = km * 0.621371
print("Miles:", round(miles, 2))Identify the problem and explain how to fix it before revealing the answer.
age = input("Age: ")
print(age + 1)age = int(input("Age: "))
print(age + 1)Compare the two snippets. Identify the changed line, run the corrected version and explain the effect.
Extension: Improve your solution to deal with unexpected input, add a second feature or display results more clearly.
Reflect: What was the hardest part? What would you test if someone else used your program?
Want extra practice? Try interactive Python tracing and debugging questions →
The value returned by input() is text, even if a student types digits. Predict what happens when you combine two inputs without conversion, and then compare it with adding int() values.
Check: input() returns a string, so int() or another suitable conversion is needed for numerical arithmetic.