Data Types: Strings, Integers, and Floats

From Script to Conversation

A hard-coded program always works with the values written into its script. An interactive program can ask the user for information, process the response, and then produce an answer. Python's input() function provides the pause between those stages: it waits for keyboard input, then gives the program what the user typed.

The Pause Before Enter

When Python reaches input(), it pauses the program and waits for the user to type on the keyboard. A prompt string can be displayed before the pause so the user knows what to enter. The program resumes after the user presses Enter. The value returned at that point is the text the user typed, represented as a string.

name = input("What is your name? ")
print("Hello, " + name)

What is your name? Alice
Hello, Alice

In this example, Python displays the prompt first. It then waits while the user types Alice and presses Enter. The returned string is stored in name, and the next print() statement uses that stored value.

Strings Before Numbers

A value returned by input() remains a string even when it looks like a number. For example, typing 15 gives input() the text "15". Python does not automatically make that text an integer merely because the characters are digits. To use the response in arithmetic, pass the returned string to int().

age = int(input("How old are you? "))
next_age = age + 1
print("Next year you will be " + str(next_age))

How old are you? 15
Next year you will be 16

The conversion can also happen in one line. In int(input("How old are you? ")), input() first waits and returns a string. The surrounding int() then converts that returned string before the value is assigned to age. This nested form is the standard concise way to obtain integer input.

Choosing the Right Conversion

• Assuming digits entered through input() are already integers

  input() returns the response as a string, even when the response consists of digits. The value has not been converted for integer arithmetic.

  Fix: Use value = int(input("Enter a number: ")) before adding 1.

• Omitting the prompt string

  The program waits for keyboard input without telling the user what to enter.

  Fix: Pass a guiding string such as input("Enter a number: ").

• Converting too late

  The response is still a string until int(value) is applied. Any arithmetic must use the converted integer.

  Fix: Convert as part of the assignment when the value is intended for arithmetic: value = int(input("Enter a number: ")).

• Treating the displayed form as proof of the data type

  The source rule concerns what input() returns: the returned value is the string "15".

  Fix: Track the conversion explicitly: input() returns a string, and int() produces an integer.

Try the Input Flow

Key Takeaways

1. input() pauses execution, displays its prompt, waits for keyboard input, and resumes after the user presses Enter.
2. The value returned by input() is always a string, including when the user types digits.
3. Use int() to convert string input into an integer for arithmetic.
4. The concise pattern int(input("prompt")) captures and converts numeric input in one line.
5. This lesson establishes strings returned by input() and integers produced by int(); it does not develop float behavior.