name = "Alex"        # str
age = 25             # int
score = 98.5         # float
is_active = True     # bool
data = None          # NoneType

# Type checking
type(name)            # <class 'str'>
isinstance(age, int)  # True

# Type casting
int("42")       # 42
str(42)         # "42"
float("3.14")   # 3.14
list("abc")     # ['a', 'b', 'c']

s = "Hello, World!"

# Methods
s.upper()          # "HELLO, WORLD!"
s.lower()          # "hello, world!"
s.strip()          # removes whitespace
s.split(", ")      # ["Hello", "World!"]
s.replace("o","0") # "Hell0, W0rld!"
s.startswith("He") # True
s.endswith("!")    # True
"lo" in s          # True

# f-strings (best way)
name = "Alex"
age = 25
f"Name: {name}, Age: {age}"  # "Name: Alex, Age: 25"
f"{3.14159:.2f}"              # "3.14"
f"{1000000:,}"                # "1,000,000"

# List — ordered, mutable
fruits = ["apple", "banana", "cherry"]
fruits.append("date")        # add to end
fruits.insert(0, "avocado")  # insert at index
fruits.pop()                 # remove last
fruits.remove("banana")      # remove by value
fruits[0]                    # first item
fruits[-1]                   # last item
fruits[1:3]                  # slice

# Tuple — ordered, immutable
coords = (10.5, 20.3)
x, y = coords               # unpacking

# Dict — key-value pairs
person = {"name": "Alex", "age": 25}
person["name"]               # "Alex"
person.get("email", "N/A")   # safe get with default
person["city"] = "NYC"       # add/update
person.keys()                # dict_keys
person.values()              # dict_values
person.items()               # dict_items

# Set — unique values
unique = {1, 2, 3, 3}        # {1, 2, 3}
unique.add(4)
unique.discard(1)
a & b  # intersection
a | b  # union
a - b  # difference

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

# Ternary
status = "adult" if age >= 18 else "minor"

# Match (Python 3.10+)
match command:
    case "quit":
        quit()
    case "hello":
        print("Hello!")
    case _:
        print("Unknown")

# For loop
for item in ["a", "b", "c"]:
    print(item)

for i in range(10):          # 0-9
    print(i)

for i, val in enumerate(["a","b","c"]):
    print(i, val)             # 0 a, 1 b, 2 c

for k, v in dict.items():
    print(k, v)

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

# Loop control
break      # exit loop
continue   # skip to next iteration
pass       # do nothing (placeholder)

# Basic function
def greet(name: str, greeting: str = "Hello") -> str:
    return f"{greeting}, {name}!"

# *args — variable positional args
def sum_all(*args):
    return sum(args)

# **kwargs — variable keyword args
def print_info(**kwargs):
    for key, val in kwargs.items():
        print(f"{key}: {val}")

# Lambda
square = lambda x: x ** 2
double = lambda x: x * 2

# Decorators
def timer(func):
    def wrapper(*args, **kwargs):
        import time
        start = time.time()
        result = func(*args, **kwargs)
        print(f"Time: {time.time() - start:.4f}s")
        return result
    return wrapper

@timer
def slow_function():
    import time
    time.sleep(1)

squares = [x**2 for x in range(10)]
evens   = [x for x in range(20) if x % 2 == 0]
pairs   = [(x, y) for x in range(3) for y in range(3)]

# Dict comprehension
squared_dict = {x: x**2 for x in range(5)}

# Set comprehension
unique_lengths = {len(w) for w in ["hi","hello","hey"]}

class Animal:
    species = "Unknown"  # class variable

    def __init__(self, name: str, age: int):
        self.name = name   # instance variable
        self.age = age

    def speak(self) -> str:
        return f"{self.name} makes a sound"

    def __repr__(self) -> str:
        return f"Animal(name={self.name!r}, age={self.age})"

class Dog(Animal):           # inheritance
    def speak(self) -> str:  # override
        return f"{self.name} says Woof!"

dog = Dog("Rex", 3)
dog.speak()  # "Rex says Woof!"

try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"Error: {e}")
except (TypeError, ValueError):
    print("Type or value error")
else:
    print("No error occurred")
finally:
    print("Always runs")

# Raise custom exception
class CustomError(Exception):
    pass

raise CustomError("Something went wrong")

# Read
with open("file.txt", "r") as f:
    content = f.read()      # full file
    lines = f.readlines()   # list of lines

# Write
with open("file.txt", "w") as f:
    f.write("Hello World\n")

# JSON
import json
data = {"key": "value"}
json.dumps(data)            # to string
json.loads('{"key": "v"}') # from string

with open("data.json", "w") as f:
    json.dump(data, f, indent=2)

len([1,2,3])               # 3
range(0, 10, 2)            # 0,2,4,6,8
map(str, [1,2,3])          # ['1','2','3']
filter(None, [0,1,None])   # [1]
zip([1,2], ['a','b'])      # [(1,'a'),(2,'b')]
sorted([3,1,2])            # [1, 2, 3]
sorted(items, key=lambda x: x.name)
enumerate(["a","b","c"])   # (0,'a'),(1,'b'),(2,'c')
any([False, True, False])  # True
all([True, True, True])    # True
min([3,1,2])               # 1
max([3,1,2])               # 3
sum([1,2,3])               # 6
abs(-5)                    # 5
round(3.14159, 2)          # 3.14