Chapter 4: User Input¶

🚀 Open Notebook¶

📺 Video Tutorial¶

User input in Python is easy + exercises ⌨️ (9:48)

📚 What You’ll Learn¶

Learn how to make your programs interactive by accepting input from users!

🎯 Learning Objectives¶

Use the input() function to get user data
Understand that input() always returns a string
Combine input() with type casting for numeric inputs
Create interactive programs that respond to user input

📖 Concept Explanation¶

The input() Function¶

The input() function is used to get information from the user. It:

Displays a message (prompt) to the user
Waits for the user to type something
Returns what the user typed as a string

Syntax¶

variable = input("Your prompt message: ")

Important: input() Always Returns a String!¶

Even if the user types a number, input() returns it as text:

age = input("Enter your age: ")  # If user types 25, age = "25" (string)
# To do math, convert it:
age = int(input("Enter your age: "))  # Now age = 25 (integer)

💡 Examples¶

Example 1: Simple Text Input¶

name = input("What is your name? ")
print(f"Hello, {name}!")

Example 2: Numeric Input¶

# Wrong way (can't do math with strings):
age = input("Enter your age: ")
# next_year = age + 1  # Error!

# Correct way:
age = int(input("Enter your age: "))
next_year = age + 1
print(f"Next year you'll be {next_year}")

Example 3: Multiple Inputs¶

first_name = input("First name: ")
last_name = input("Last name: ")
age = int(input("Age: "))

print(f"Hello {first_name} {last_name}, you are {age} years old!")

Example 4: Float Input¶

height = float(input("Enter your height in meters: "))
print(f"Your height is {height}m")

✍️ Practice Exercises¶

Create a program that asks for the user’s name and favorite color, then prints them
Make a program that asks for two numbers and prints their sum
Ask for a user’s birth year and calculate their age (assume current year is 2025)
Create a mad libs style program that asks for several words and creates a story
Ask for temperature in Celsius and convert it to Fahrenheit

🔍 Common Mistakes¶

Mistake 1: Forgetting Type Conversion¶

# Wrong:
age = input("Age: ")  # age is "25" (string)
print(age + 1)  # Error! Can't add string and number

# Correct:
age = int(input("Age: "))  # age is 25 (integer)
print(age + 1)  # Works! Prints 26

Mistake 2: Wrong Conversion Type¶

# If user enters "3.14":
number = int(input("Enter number: "))  # Error! Can't convert "3.14" to int

# Use float() instead:
number = float(input("Enter number: "))  # Works! number = 3.14

Mistake 3: Forgetting the Prompt¶

name = input()  # Works but user doesn't know what to enter
name = input("Enter your name: ")  # Better! Clear instruction

📝 Input Patterns¶

Pattern 1: Input on Same Line as Conversion¶

age = int(input("Enter age: "))

Pattern 2: Input Then Convert (easier to debug)¶

age_str = input("Enter age: ")
age = int(age_str)

Pattern 3: Input with Validation (advanced)¶

age = input("Enter age: ")
if age.isdigit():  # Check if input is a number
    age = int(age)
    print(f"You are {age} years old")
else:
    print("Please enter a valid number")

🎮 Interactive Program Example¶

# Simple greeting program
name = input("What's your name? ")
age = int(input("How old are you? "))
city = input("Where do you live? ")

print(f"\nNice to meet you, {name}!")
print(f"You are {age} years old and live in {city}.")
print("Welcome to Python programming!")

🚀 Try It Yourself¶

Create an interactive program that:

Asks the user for their name
Asks for their favorite number (integer)
Asks for their favorite food
Creates a personalized message using all the information

🎓 Key Takeaways from Video¶

Functions are reusable blocks of code
Use if-elif-else for conditional logic
Follow along with the video for hands-on practice

💡 These points cover the main concepts from the video tutorial to help reinforce your learning.

🔗 Next Chapter¶

Continue to Chapter 5: Madlibs Game to create a fun word game using user input!