Python Tutorial — Learn Python Step by Step

# Variables are created on first assignment (no declaration needed)
name = "Alice"          # str
age = 25                # int
height = 5.7            # float
is_student = True       # bool
grades = [90, 85, 92]   # list

# Print values and their types
print(name, type(name))         # Alice <class 'str'>
print(age, type(age))           # 25 <class 'int'>
print(height, type(height))     # 5.7 <class 'float'>
print(is_student, type(is_student))  # True <class 'bool'>

# Multiple assignment
x, y, z = 1, 2, 3
a = b = c = 0  # all point to 0

# Swap values (no temp variable needed!)
x, y = y, x
print(x, y)  # 2 1

# Integers (no size limit in Python!)
decimal = 42
negative = -100
big = 1_000_000       # underscores for readability
binary = 0b1010       # 10
octal = 0o17          # 15
hexadecimal = 0xFF    # 255

# Floats
pi = 3.14159
scientific = 2.5e3    # 2500.0
tiny = 1.2e-4         # 0.00012

# Complex numbers
z = 3 + 4j
print(z.real, z.imag)  # 3.0 4.0

# Boolean (subclass of int)
print(True + True)     # 2
print(False * 10)      # 0

# Single and double quotes are identical
s1 = 'Hello'
s2 = "Hello"

# Triple quotes for multi-line strings
message = """This is a
multi-line string
that preserves newlines."""

# Raw strings (no escape processing)
path = r"C:\Users\name\folder"  # backslashes are literal

# f-strings for formatting
name = "World"
greeting = f"Hello, {name}!"

# String operations
print(len(greeting))         # 13
print(greeting.upper())      # HELLO, WORLD!
print(greeting[0:5])         # Hello

# Python has no true constants — it is a CONVENTION to use UPPER_CASE
MAX_SIZE = 100
PI = 3.14159
DATABASE_URL = "postgresql://localhost/mydb"

# Nothing stops reassignment (but tools like mypy can warn)
# MAX_SIZE = 200  # works but violates convention