Variables & Data Types

# No type declarations needed
name = "Alice"       # str
age = 25             # int
height = 1.68        # float
is_student = True    # bool

# Dynamic typing — variables can change type
value = 42           # int
value = "now text"   # str — perfectly valid

# Integer
count = 100
binary = 0b1010      # 10 in decimal
hex_val = 0xFF       # 255 in decimal

# Float
pi = 3.14159
scientific = 1.5e-4  # 0.00015

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

# Type conversion
int("42")           # 42
float("3.14")       # 3.14
round(3.14159, 2)   # 3.14

is_ready = True
is_done = False

# Boolean from comparisons
print(5 > 3)    # True
print(10 == 9)  # False

# Truthy/falsy values
bool(0)          # False
bool("")         # False
bool([])         # False
bool(42)         # True
bool("hello")    # True

result = None  # Represents absence of a value

# Common pattern: initialize then assign
user = None
# ... later ...
user = get_user()  # might return None
if user is None:
    print("User not found")

type(42)           # <class 'int'>
type("hello")      # <class 'str'>
type(True)         # <class 'bool'>

# Check with isinstance() — preferred
isinstance(42, int)          # True
isinstance("hi", (str, int)) # True — checks against tuple of types

def greet(name: str) -> str:
    return f"Hello, {name}"

age: int = 25
# Type hint is ignored at runtime:
age = "twenty-five"  # No error!

a = [1, 2, 3]
b = a          # b references the SAME list
b.append(4)
print(a)       # [1, 2, 3, 4] — a changed too!

# Create a copy instead
c = a.copy()
c.append(5)
print(a)       # [1, 2, 3, 4] — unchanged