Python Basics

Quick reference guide for Python fundamentals.

Variables and Data Types

Python is dynamically typed (no need to declare types):

# ========== Numbers ==========
age = 25              # Integer
price = 19.99         # Float (decimal)
distance = 1e6        # Scientific notation (1,000,000)

# ========== Strings ==========
name = "Yudi"         # Double quotes
message = 'Hello!'    # Single quotes (same as double)
multiline = """
This is a
multi-line string
"""

# ========== Booleans ==========
is_active = True      # Note: capital T and F
has_permission = False

# ========== Lists (ordered, mutable) ==========
fruits = ["apple", "banana", "orange"]
mixed = [1, "two", 3.0, True]  # Can mix types

# ========== Dictionaries (key-value pairs) ==========
person = {
    "name": "Yudi",
    "age": 25,
    "city": "Jakarta"
}
# Access: person["name"] → "Yudi"

# ========== Tuples (ordered, immutable) ==========
coordinates = (10, 20)  # Cannot be changed after creation

# ========== Sets (unordered, unique values) ==========
unique_numbers = {1, 2, 3, 3, 2}  # Becomes {1, 2, 3}

Control Flow

If Statements

age = 18

if age >= 18:
    print("Adult")
elif age >= 13:
    print("Teenager")
else:
    print("Child")

Loops

# For loop
for i in range(5):
    print(i)

# While loop
count = 0
while count < 5:
    print(count)
    count += 1

# List iteration
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
    print(fruit)

Functions

Define reusable code blocks to avoid repetition:

# ========== Basic Function ==========
def greet(name):
    """Greet a person by name"""
    return f"Hello, {name}!"

# ========== Multiple Parameters ==========
def add(a, b):
    """Add two numbers together"""
    return a + b

# ========== Default Parameters ==========
def power(base, exponent=2):
    """Raise base to exponent (defaults to square)"""
    return base ** exponent

# ========== Multiple Return Values ==========
def get_user():
    """Return multiple values as tuple"""
    return "Yudi", 25, "Jakarta"

# ========== Variable Arguments ==========
def sum_all(*numbers):
    """Sum any number of arguments"""
    return sum(numbers)

# ========== Calling Functions ==========
message = greet("Yudi")           # "Hello, Yudi!"
result = add(5, 3)                # 8
squared = power(5)                # 25 (uses default exponent=2)
cubed = power(5, 3)               # 125
name, age, city = get_user()      # Unpack tuple
total = sum_all(1, 2, 3, 4, 5)    # 15

List Comprehensions

Create lists efficiently in one line (Pythonic way):

# ========== Basic Comprehension ==========
# Traditional way:
squares = []
for x in range(10):
    squares.append(x**2)

# Comprehension way (better):
squares = [x**2 for x in range(10)]
# Result: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# ========== With Condition (Filter) ==========
# Get only even numbers
evens = [x for x in range(20) if x % 2 == 0]
# Result: [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# ========== Transform and Filter ==========
# Square even numbers only
even_squares = [x**2 for x in range(10) if x % 2 == 0]
# Result: [0, 4, 16, 36, 64]

# ========== Nested Comprehension (Matrix) ==========
# Create 3x3 multiplication table
matrix = [[i*j for j in range(3)] for i in range(3)]
# Result: [[0,0,0], [0,1,2], [0,2,4]]

# ========== String Operations ==========
# Convert to uppercase
names = ["alice", "bob", "charlie"]
upper_names = [name.upper() for name in names]
# Result: ["ALICE", "BOB", "CHARLIE"]

Common Methods

String Methods

text = "Hello, World!"

text.lower()          # "hello, world!"
text.upper()          # "HELLO, WORLD!"
text.replace("Hello", "Hi")  # "Hi, World!"
text.split(",")       # ["Hello", " World!"]

List Methods

numbers = [1, 2, 3]

numbers.append(4)     # [1, 2, 3, 4]
numbers.extend([5, 6]) # [1, 2, 3, 4, 5, 6]
numbers.pop()         # Removes last item
numbers.sort()        # Sorts in place

Tips

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