Chapter 3: Type Casting¶
🚀 Open Notebook¶
📺 Video Tutorial¶
Learn type casting in 7 minutes! 💱 (7:39)
📚 What You’ll Learn¶
Type casting is the process of converting data from one type to another - essential for working with user input and performing calculations!
🎯 Learning Objectives¶
Understand what type casting is and why it’s needed
Learn to convert between int, float, str, and bool
Use the
type()function to check data typesHandle common type conversion scenarios
📖 Concept Explanation¶
What is Type Casting?¶
Type casting (or type conversion) is the process of converting a variable from one data type to another.
Why is Type Casting Needed?¶
User input is always a string, even if you enter numbers
Mathematical operations require numeric types
String concatenation requires all values to be strings
Different operations work with different types
Common Type Casting Functions¶
int() - Convert to Integer¶
float_num = 3.14
int_num = int(float_num) # Result: 3 (decimal is removed)
text = "25"
number = int(text) # Result: 25 (string becomes integer)
float() - Convert to Float¶
int_num = 25
float_num = float(int_num) # Result: 25.0
text = "3.14"
number = float(text) # Result: 3.14
str() - Convert to String¶
age = 25
age_text = str(age) # Result: "25"
price = 19.99
price_text = str(price) # Result: "19.99"
bool() - Convert to Boolean¶
number = 1
is_true = bool(number) # Result: True (any non-zero number is True)
empty_string = ""
is_false = bool(empty_string) # Result: False (empty strings are False)
The type() Function¶
The type() function tells you what data type a variable is:
name = "Alice"
age = 25
print(type(name)) # Output: <class 'str'>
print(type(age)) # Output: <class 'int'>
💡 Examples¶
Example 1: Converting User Input¶
# input() always returns a string
age_str = input("Enter your age: ") # If user types "25", age_str = "25"
age_int = int(age_str) # Convert to integer: 25
print(age_int + 5) # Now we can do math: 30
Example 2: String Concatenation¶
age = 25
# This doesn't work: print("I am " + age) # Error!
print("I am " + str(age)) # Works! Convert age to string first
# Or use f-strings (no conversion needed):
print(f"I am {age}") # Also works!
Example 3: Float to Int¶
gpa = 3.7
gpa_int = int(gpa) # Result: 3 (truncates, doesn't round)
print(gpa_int)
✍️ Practice Exercises¶
Ask the user for two numbers and add them (remember to convert from string to int)
Create a float variable and convert it to int, then to string
Ask user for their height in meters (float) and convert it to centimeters (int)
Create a program that asks for a price (string) and adds 10% tax, displaying the result
🔍 Common Mistakes¶
Forgetting to Convert User Input¶
# Wrong:
age = input("Enter age: ")
print(age + 5) # Error! Can't add string and number
# Correct:
age = int(input("Enter age: "))
print(age + 5) # Works!
Trying to Convert Invalid Strings¶
# This will cause an error:
text = "hello"
number = int(text) # Error! Can't convert "hello" to int
# Only numeric strings can be converted:
text = "123"
number = int(text) # Works! Result: 123
Losing Precision¶
pi = 3.14159
pi_int = int(pi) # Result: 3 (decimal part is lost forever!)
📝 Key Points¶
input()always returns a string, even if the user types a numberint()truncates decimals (doesn’t round):int(3.9)→3You can’t convert non-numeric strings to numbers:
int("hello")→ ErrorType casting is permanent for that variable unless you reassign it
🚀 Try It Yourself¶
Modify main.py to create a program that:
Asks for a person’s name (string)
Asks for their age (convert to int)
Asks for their height in meters (convert to float)
Displays all information with proper types
🎓 Key Takeaways from Video¶
Strings are text data enclosed in quotes
Follow along with the video for hands-on practice
Experiment with the code examples to deepen understanding
💡 These points cover the main concepts from the video tutorial to help reinforce your learning.
🔗 Next Chapter¶
Continue to Chapter 4: User Input to learn how to interact with users!