User Input

5 min · The Basics

Getting User Input

The input() function is Python's way of getting data from the user. When your program encounters input(), it pauses execution and waits for the user to type something and press Enter.

Important: The input() function always returns a string, even if the user types a number. You must convert it if you need a different type.

input.py
# Basic input usage
name = input("What is your name? ")
# Program waits here until user types and presses Enter
print(f"Hello, {name}!")

# Input with empty prompt (just waits)
response = input()  # No prompt shown, just waits

# Multiple inputs
first_name = input("First name: ")
last_name = input("Last name: ")
print(f"Full name: {first_name} {last_name}")

Converting Input

Since input() always returns a string, you need to convert it when you want to do mathematical operations or need a different data type:

input_conversion.py
# Get age as string, convert to integer
age_str = input("Enter your age: ")
age = int(age_str)  # Convert string to int
birth_year = 2024 - age
print(f"You were born in {birth_year}")

# Get price as string, convert to float
price_str = input("Enter price: ")
price = float(price_str)  # Convert string to float
total = price * 1.08  # Add 8% tax
print(f"Total with tax: ${total:.2f}")

Handling Multiple Inputs

You can get multiple inputs from the user in sequence:

multiple_inputs.py
# Collecting multiple values
name = input("Enter your name: ")
age = int(input("Enter your age: "))
height = float(input("Enter your height (feet): "))

print(f"\nName: {name}")
print(f"Age: {age}")
print(f"Height: {height} feet")

# Getting input and immediately converting
num1 = int(input("First number: "))
num2 = int(input("Second number: "))
print(f"{num1} + {num2} = {num1 + num2}")

Input Validation

It's important to validate user input to handle errors gracefully. Users might enter invalid data:

validation.py
# Safe input with validation
while True:
    age_input = input("Enter your age: ")
    if age_input.isdigit():  # Check if all characters are digits
        age = int(age_input)
        if age > 0 and age < 120:
            break
        else:
            print("Please enter a valid age (0-120)")
    else:
        print("Please enter a number")

print(f"You entered: {age}")

# Using try/except for safer conversion
try:
    price = float(input("Enter price: $"))
    print(f"Price: ${price:.2f}")
except ValueError:
    print("Invalid price format!")

Practical Examples

Here are some real-world examples of using input:

practical.py
# Simple calculator
num1 = float(input("Enter first number: "))
num2 = float(input("Enter second number: "))
operator = input("Enter operation (+, -, *, /): ")

if operator == "+":
    result = num1 + num2
elif operator == "-":
    result = num1 - num2
elif operator == "*":
    result = num1 * num2
elif operator == "/":
    result = num1 / num2
else:
    result = "Invalid operator"

print(f"Result: {result}")

# User profile
username = input("Enter username: ")
email = input("Enter email: ")
age = int(input("Enter age: "))

print(f"\nProfile Created!")
print(f"Username: {username}")
print(f"Email: {email}")
print(f"Age: {age}")

Input Best Practices

✅ Good Practices

• Always provide clear prompts that tell users what to enter

• Validate input before using it

• Convert input to the correct type immediately after receiving it

• Handle errors with try/except blocks

• Give users clear error messages if input is invalid

❌ Common Mistakes

• Forgetting that input() returns a string

• Not converting numeric input before doing math

• Not validating user input

• Using input() in a loop without validation (can cause infinite loops)

📝 Note for This Environment

In this web-based learning environment, input() doesn't work interactively. We simulate it with pre-defined values. In a real Python environment (like running Python from the terminal), input() will pause your program and wait for keyboard input!

🎉

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