Python Data Types

Hey, new coder! Welcome to Python! You’ve already learned about variables, which are like labeled boxes for storing stuff. But what kinds of stuff can you store? That’s where data types come in! Data types tell Python whether you’re storing a number, text, or something else. This guide is super beginner-friendly, with lots of examples (good and bad ones!) to help you understand Python’s built-in data types, how to check them, and how to set them. Let’s dive in!

Data types are like different types of toys—each one works differently and is used for different things!

1. What Are Data Types?

In programming, a data type tells Python what kind of information a variable holds. For example, is it a number, a word, or a list of things? Different data types let you do different things, like adding numbers or combining words. Python makes it easy because it automatically figures out the data type when you assign a value to a variable.

Valid Example:

Example

name = "Alice" # Text (string) age = 12 # Whole number (integer) height = 1.5 # Decimal number (float) print(name, age, height) # Prints: Alice 12 1.5

Invalid Example (mixing types incorrectly):

Example

name = "Alice" age = 12 print(name + age) # Error: Can’t combine text and number without converting

Each data type has its own rules, like how you can’t add a number to a word without turning the number into text first!

2. Python’s Built-in Data Types

Python has lots of built-in data types, grouped into categories. As a beginner, you’ll mostly use a few, but here’s the full list so you know what’s possible:

• Text Type: str (for words or sentences)
• Numeric Types: int (whole numbers), float (decimals), complex (advanced numbers)
• Sequence Types: list (changeable list), tuple (unchangeable list), range (number sequences)
• Mapping Type: dict (key-value pairs, like a dictionary)
• Set Types: set (unique items), frozenset (unchangeable set)
• Boolean Type: bool (True or False)
• Binary Types: bytes, bytearray, memoryview (for advanced use)
• None Type: NoneType (represents "nothing")

Let’s look at examples of the most common ones for beginners!

Text Type: str

Strings hold text, like names or messages, and use single (') or double (") quotes.

Valid Example:

Example

greeting = "Hello, World!" # String print(greeting) # Prints: Hello, World!

Invalid Example (missing quotes):

Example

greeting = Hello # Error: Text needs quotes print(greeting)

Numeric Types: int, float, complex

Integers (int) are whole numbers, floats (float) are decimals, and complex numbers (complex) are for advanced math.

Valid Example:

Example

score = 100 # Integer price = 9.99 # Float complex_num = 1j # Complex print(score, price, complex_num) # Prints: 100 9.99 1j

Invalid Example (invalid number format):

Example

price = 9.9.9 # Error: Invalid decimal format print(price)

Integers are for counting (like 5 apples), floats are for measurements (like 1.5 meters), and complex numbers are for math wizards!

Sequence Types: list, tuple, range

Lists hold multiple items you can change, tuples hold items you can’t change, and ranges create number sequences.

Valid Example:

Example

fruits = ["apple", "banana", "cherry"] # List colors = ("red", "blue", "green") # Tuple numbers = range(6) # Range (0 to 5) print(fruits, colors, list(numbers)) # Prints: ['apple', 'banana', 'cherry'] ('red', 'blue', 'green') [0, 1, 2, 3, 4, 5]

Invalid Example (wrong list syntax):

Example

fruits = [apple, banana, cherry] # Error: Items need quotes for strings print(fruits)

Mapping Type: dict

Dictionaries store key-value pairs, like a real dictionary with words and meanings.

Valid Example:

Example

person = {"name": "John", "age": 36} # Dictionary print(person) # Prints: {'name': 'John', 'age': 36}

Invalid Example (missing key-value syntax):

Example

person = {name: John} # Error: Keys and values need quotes for strings print(person)

Set Types: set, frozenset

Sets store unique items (no duplicates), and frozensets are sets you can’t change.

Valid Example:

Example

fruits = {"apple", "banana", "cherry"} # Set frozen_fruits = frozenset({"apple", "banana", "cherry"}) # Frozenset print(fruits, frozen_fruits) # Prints: {'banana', 'apple', 'cherry'} frozenset({'banana', 'apple', 'cherry'})

Invalid Example (duplicates in set):

Example

fruits = {"apple", "apple", "banana"} # Set removes duplicates automatically print(fruits) # Prints: {'apple', 'banana'}

Boolean Type: bool

Booleans are True or False, great for yes/no questions.

Valid Example:

Example

is_student = True # Boolean has_pet = False # Boolean print(is_student, has_pet) # Prints: True False

Invalid Example (using string instead of boolean):

Example

is_student = "True" # Not a boolean, it’s a string! print(is_student) # Prints: True (but it’s text, not a boolean)

Binary Types: bytes, bytearray, memoryview

These are for advanced stuff like handling raw data (don’t worry about them yet!).

Valid Example:

Example

data = b"Hello" # Bytes array = bytearray(5) # Bytearray view = memoryview(bytes(5)) # Memoryview print(data, array, view) # Prints: b'Hello' bytearray(b'\x00\x00\x00\x00\x00') <memory at ...>

Invalid Example (wrong bytes syntax):

Example

data = b'Hello' # Valid data = b"Hello World" # Error: Bytes don’t allow spaces without special handling print(data)

None Type: NoneType

None means "nothing" and is used when a variable has no value.

Valid Example:

Example

result = None # No value print(result) # Prints: None

Invalid Example (misusing None):

Example

result = None print(result + 5) # Error: Can’t add None to a number

As a beginner, focus on strings, integers, floats, booleans, and lists—they’re the most common!

3. Getting the Data Type

You can check a variable’s data type using the type() function. It’s like asking, “What’s in this box?”

Valid Example:

Example

x = 5 print(type(x)) # Prints: <class 'int'> y = "Hello" print(type(y)) # Prints: <class 'str'>

Invalid Example (checking undefined variable):

Example

print(type(z)) # Error: z is not defined

Use type() when you’re curious or debugging to make sure your variable is the right type!

4. Setting the Data Type

In Python, the data type is set automatically when you assign a value to a variable. For example:

Valid Examples:

Example

x = "Hello World" # str x = 20 # int x = 20.5 # float x = ["apple", "banana", "cherry"] # list x = True # bool x = None # NoneType print(x) # Prints: None (last assignment)

Invalid Example (incorrect value for type):

Example

x = [1, 2, 3 # Error: Missing closing bracket print(x)

5. Setting the Specific Data Type

You can force a specific data type using constructor functions, like str() or int(). This is useful when you need to convert data.

Valid Examples:

Example

x = str("Hello World") # str x = int(20) # int x = float(20.5) # float x = list(("apple", "banana", "cherry")) # list x = bool(5) # bool (non-zero numbers are True) print(x) # Prints: True

Invalid Example (invalid conversion):

Example

x = int("Hello") # Error: Can’t turn text into a number print(x)

Constructors like str() or int() are like magic wands to change one type to another, but they only work if the change makes sense!

6. Exercises to Practice Data Types

Let’s try some fun exercises to practice data types! These are beginner-friendly, with valid and invalid examples.

Exercise 1: Create Variables with Different Types

Make variables for a pet’s name (string), age (integer), weight (float), and if it’s happy (boolean). Print them.

Solution:

Example

""" Stores and prints info about a pet """ pet_name = "Buddy" # String pet_age = 3 # Integer pet_weight = 5.5 # Float is_happy = True # Boolean print(pet_name, "is", pet_age, "years old, weighs", pet_weight, "kg, and is happy:", is_happy)

Invalid Attempt:

Example

pet_name = Buddy # Error: String needs quotes print(pet_name)

Exercise 2: Check Data Types

Create a variable for a score and a list of fruits, then use type() to check their types.

Solution:

Example

score = 95 # Integer fruits = ["apple", "banana"] # List print(type(score)) # Prints: <class 'int'> print(type(fruits)) # Prints: <class 'list'>

Invalid Attempt:

Example

print(type(unknown)) # Error: Variable not defined

Exercise 3: Convert Data Types

Ask for a user’s age as input (string), convert it to an integer, and add 5 years.

Solution:

Example

age = int(input("Enter your age: ")) # Convert string input to integer future_age = age + 5 print("In 5 years, you’ll be", future_age) # Prints age + 5

Invalid Attempt:

Example

age = input("Enter your age: ") # String future_age = age + 5 # Error: Can’t add string and number print(future_age)

Common Mistakes to Avoid

As a beginner, here are some variable-related mistakes to watch out for:

1. Using Invalid Names: Don’t start variable names with numbers or use spaces:
   Python

   # Bad: Invalid variable names 2score = 100 # Starts with a number first name = "Alice" # Contains a space # Good: Valid variable names score = 100 first_name = "Alice"
2. Forgetting to Assign a Value: You must assign a value to a variable before using it, or you’ll get an error:
   Python

   # Bad: Using a variable before assigning print(my_variable) # Error: my_variable is not defined # Good: Assign first, then use my_variable = "Hello" print(my_variable)
3. Mixing Data Types Incorrectly: Be careful when combining different types, like strings and numbers:
   Python

   # Bad: Mixing types causes an error age = 15 print("Age: " + age) # Error: can't concatenate string and integer # Good: Convert the number to a string age = 15 print("Age: " + str(age))

Practice Time!

Let’s try using variables! Below is a simple Python program. Add variables and comments to make it clearer, then check your work.

Program:

Python

print("Enter your name: ") print("Hello, " + input() + "!") print("How old are you? ") print("You are " + input() + " years old.")

Your Task: Rewrite the program using variables for the name and age, and add comments to explain each line. Here’s an example solution:

Python

""" This program asks for the user’s name and age, then prints a personalized greeting. """ name = input("Enter your name: ") # Store the user’s name print("Hello, " + name + "!") # Print a greeting with the name age = input("How old are you? ") # Store the user’s age print("You are " + age + " years old.") # Print the user’s age

Try rewriting the program with variables and compare it to this example. Did you use clear variable names and add helpful comments?

What’s Next?

Great job! You now know Python’s data types and how to use them. You’ve seen what works and what doesn’t, so you’re ready to avoid common mistakes. Try making your own programs, like a shopping list (using lists) or a true/false quiz (using booleans). Next, you might learn about conditionals (if statements) or loops to make your code even cooler!

Have fun coding, and keep experimenting with different data types!