Python Data Types

Python Programming

Python Data Types

Beginner Lesson 3 of 10

Python Data Types

In this lesson, we’ll explore Python’s collection data types that help you organize and store multiple values.

Lists

Lists are ordered, mutable collections that can hold items of different types.

# Creating lists
fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]
empty_list = []

# Accessing elements (0-indexed)
print(fruits[0])   # "apple"
print(fruits[-1])  # "cherry" (last item)
print(fruits[1:3]) # ["banana", "cherry"] (slicing)

# Modifying lists
fruits[0] = "mango"        # Change element
fruits.append("orange")    # Add to end
fruits.insert(1, "grape")  # Insert at position
fruits.remove("banana")    # Remove by value
popped = fruits.pop()      # Remove and return last
del fruits[0]              # Delete by index

# List operations
numbers = [3, 1, 4, 1, 5]
numbers.sort()             # Sort in place: [1, 1, 3, 4, 5]
numbers.reverse()          # Reverse in place: [5, 4, 3, 1, 1]
print(len(numbers))        # Length: 5
print(sum(numbers))        # Sum: 14
print(min(numbers))        # Minimum: 1
print(max(numbers))        # Maximum: 5

# List comprehension
squares = [x**2 for x in range(5)]  # [0, 1, 4, 9, 16]
evens = [x for x in range(10) if x % 2 == 0]  # [0, 2, 4, 6, 8]

Tuples

Tuples are ordered, immutable collections - once created, they cannot be modified.

# Creating tuples
coordinates = (10, 20)
rgb = (255, 128, 0)
single = (42,)  # Note the comma for single-element tuple

# Accessing elements
print(coordinates[0])  # 10
x, y = coordinates     # Tuple unpacking

# Tuples are immutable
# coordinates[0] = 5  # Error! Cannot modify

# When to use tuples
# - For data that shouldn't change (coordinates, RGB values)
# - As dictionary keys
# - For function return values
def get_user():
    return ("Alice", 25, "alice@email.com")

name, age, email = get_user()

Dictionaries

Dictionaries store key-value pairs for fast lookups.

# Creating dictionaries
person = {
    "name": "Alice",
    "age": 25,
    "city": "New York"
}

# Accessing values
print(person["name"])         # "Alice"
print(person.get("age"))      # 25
print(person.get("country", "Unknown"))  # "Unknown" (default)

# Modifying dictionaries
person["email"] = "alice@email.com"  # Add new key
person["age"] = 26                    # Update existing
del person["city"]                    # Delete key
person.pop("email")                   # Remove and return

# Dictionary methods
print(person.keys())    # dict_keys(['name', 'age'])
print(person.values())  # dict_values(['Alice', 26])
print(person.items())   # dict_items([('name', 'Alice'), ('age', 26)])

# Iterating over dictionaries
for key in person:
    print(f"{key}: {person[key]}")

for key, value in person.items():
    print(f"{key}: {value}")

# Dictionary comprehension
squares = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

Sets

Sets are unordered collections of unique elements.

# Creating sets
fruits = {"apple", "banana", "cherry"}
numbers = {1, 2, 3, 3, 3}  # Duplicates removed: {1, 2, 3}
empty_set = set()  # Note: {} creates empty dict, not set

# Set operations
fruits.add("orange")
fruits.remove("banana")  # Raises error if not found
fruits.discard("mango")  # No error if not found

# Set mathematics
a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

print(a | b)  # Union: {1, 2, 3, 4, 5, 6}
print(a & b)  # Intersection: {3, 4}
print(a - b)  # Difference: {1, 2}
print(a ^ b)  # Symmetric difference: {1, 2, 5, 6}

# Membership testing (very fast)
print(3 in a)  # True

Comparison Summary

Feature	List	Tuple	Dictionary	Set
Ordered	✅	✅	✅*	❌
Mutable	✅	❌	✅	✅
Duplicates	✅	✅	Keys: ❌	❌
Indexing	✅	✅	By key	❌
Syntax	[]	()	{}	{}

*Dictionaries maintain insertion order since Python 3.7

Practice Exercises

Exercise 1: List Manipulation

Remove duplicates from a list while preserving order.

numbers = [1, 3, 2, 3, 1, 4, 2, 5]
# Expected: [1, 3, 2, 4, 5]

Exercise 2: Word Counter

Count the frequency of each word in a sentence.

sentence = "the quick brown fox jumps over the lazy dog"
# Expected: {"the": 2, "quick": 1, ...}

Next Steps

Continue to Control Flow →