User Input in Python

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User Input in Python

Python allows programs to interact with users by accepting input at runtime.

This makes programs dynamic, interactive, and more useful.

The built-in input() function is used to read data entered by the user.

Basic User Input

When Python encounters the input() function, program execution pauses until the user types something and presses Enter.

Example: Read and Display User Input

username = input() print(f"Welcome, {username}!")

Output:

John
Welcome, John!

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Using a Prompt Message

You can display a message directly inside the input() function.

This shows the message and waits for user input on the same line.

Example: Input with Prompt

username = input("Please enter your username: ") print(f"Hello, {username}")

Output:

Please enter your username: Emma
Hello, Emma

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Taking Multiple Inputs

A program can request multiple inputs.

Python pauses at each input() call until the user responds.

Example: Multiple User Inputs

city = input("Which city do you live in? ") food = input("What is your favorite food? ") year = input("Which year were you born? ") print(f"You live in {city}, love {food}, and were born in {year}.")

Output:

Which city do you live in? Chennai
What is your favorite food? Biryani
Which year were you born? 1998
You live in Chennai, love Biryani, and were born in 1998.

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Input Is Always a String

Data received using input() is always of type string, even if the user enters numbers.

To perform calculations, you must convert the input to a numeric type such as int() or float().

Example: Convert Input to Number

radius = input("Enter the radius of the circle: ") area = 3.14 * float(radius) ** 2 print(f"Circle area: {area:.2f}")

Output:

Enter the radius of the circle: 5
Circle area: 78.50

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Validating User Input

User input should always be validated to prevent errors.

If a user enters invalid data, the program should handle it gracefully instead of crashing.

Example: Validate Numeric Input

while True: value = input("Enter a valid number: ") try: number = float(value) break except ValueError: print("Invalid input. Please enter a numeric value.") print("Input accepted. Thank you!")

Output:

Enter a valid number: python
Invalid input. Please enter a numeric value.
Enter a valid number: 42
Input accepted. Thank you!

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Why Input Validation Matters

• Prevents runtime errors
• Improves user experience
• Makes programs more reliable
• Helps handle unexpected user behavior

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