Day 3: input() and Type Casting

Quick Answer

What You Will Learn

• input() asks the user for data and always returns a str, even for numbers.
• int("21") converts text to the whole number 21. float("3.5") converts to 3.5.
• str(10) converts a number back to text "10", and bool("") is False.
• Casting is the name for changing a value from one type to another.
• In a real program you write age = int(input("Age? ")) so the age can be used in maths.

Code

age_text = "21"
print(age_text, type(age_text))
age = int(age_text)
print(age, type(age))
print(age + 1)
print(float("3.5"), str(10), bool(""))

Output

21 <class 'str'>
21 <class 'int'>
22
3.5 10 False

Code Explained, Line by Line

1. input() asks the user for data and always returns a str, even for numbers.
2. int("21") converts text to the whole number 21. float("3.5") converts to 3.5.
3. str(10) converts a number back to text "10", and bool("") is False.
4. Casting is the name for changing a value from one type to another.
5. In a real program you write age = int(input("Age? ")) so the age can be used in maths.

Real-Life Use

Every form, calculator and signup page reads input as text first and converts it before calculating.

Test Yourself — MCQs

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