# Variables (no type declaration needed)
name = "Alice"
age = 25
height = 5.7
is_student = True
nothing = None

# Type checking
type(name)         # 
isinstance(age, int) # True

# Type conversion
int("42")          # 42
float("3.14")      # 3.14
str(100)           # "100"
bool(0)            # False

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

# Print
print("Hello", name, sep=", ", end="!\n")

10 + 3   # 13  addition
10 - 3   # 7   subtraction
10 * 3   # 30  multiplication
10 / 3   # 3.333 division (float)
10 // 3  # 3   floor division
10 % 3   # 1   modulo
10 ** 3  # 1000 exponent

import math
math.sqrt(16)    # 4.0
math.ceil(3.2)   # 4
math.floor(3.8)  # 3
math.pi          # 3.14159...
math.pow(2, 8)   # 256.0
abs(-5)          # 5
round(3.7)       # 4
max(1,2,3)       # 3
min(1,2,3)       # 1

s = "Hello World"

len(s)           # 11
s.upper()        # "HELLO WORLD"
s.lower()        # "hello world"
s.strip()        # remove leading/trailing spaces
s.lstrip()       # left strip
s.rstrip()       # right strip
s.replace("World","Python") # "Hello Python"
s.split(" ")     # ["Hello","World"]
s.startswith("He") # True
s.endswith("ld") # True
s.find("World")  # 6 (index or -1)
s.count("l")     # 3
s.isdigit()      # False
s.isalpha()      # False

# f-string (recommended)
name = "Alice"
print(f"Hello, {name}! Age: {25*1}")

# Slicing
s[0:5]   # "Hello"
s[-5:]   # "World"
s[::-1]  # reverse

" ".join(["a","b","c"]) # "a b c"

score = 85

if score >= 90:
    print("A")
elif score >= 70:
    print("B")
else:
    print("F")

# One-liner ternary
result = "pass" if score >= 50 else "fail"

# Logical operators
if age >= 18 and has_id:
    print("allowed")

if not is_banned:
    print("welcome")

# for loop
for i in range(5):       # 0,1,2,3,4
    print(i)

for i in range(1, 10, 2): # 1,3,5,7,9
    print(i)

# for with enumerate
for i, item in enumerate(["a","b","c"]):
    print(i, item)

# for with zip
for a, b in zip([1,2,3], ["x","y","z"]):
    print(a, b)

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

# break / continue / else
for i in range(10):
    if i == 5: break
    if i % 2 == 0: continue
    print(i)

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

# *args (variable positional)
def total(*args):
    return sum(args)
total(1, 2, 3)  # 6

# **kwargs (variable keyword)
def show(**kwargs):
    for k, v in kwargs.items():
        print(f"{k}: {v}")

# Lambda (anonymous)
square = lambda x: x ** 2
add    = lambda a, b: a + b

# Type hints (Python 3.5+)
def add(a: int, b: int) -> int:
    return a + b

nums = [3, 1, 4, 1, 5, 9]

nums.append(2)      # add to end
nums.insert(0, 0)   # insert at index
nums.extend([6,7])  # extend with list
nums.remove(1)      # remove first occurrence
nums.pop()          # remove & return last
nums.pop(0)         # remove at index
nums.index(5)       # get index
nums.count(1)       # count occurrences
nums.sort()         # sort in place
nums.sort(reverse=True)
nums.reverse()      # reverse in place
nums.clear()        # empty the list
len(nums)           # length
sum(nums)           # sum

sorted(nums)        # returns new sorted list
list(reversed(nums))# returns new reversed list

# Tuple (immutable)
t = (1, 2, 3)
t[0]   # 1

person = {"name": "Alice", "age": 25}

person["name"]         # "Alice"
person.get("age", 0)   # 25 (with default)
person["city"] = "NYC" # add/update
del person["age"]      # delete key
"name" in person       # True

person.keys()          # dict_keys(["name","city"])
person.values()        # dict_values(["Alice","NYC"])
person.items()         # dict_items([...])

# Loop
for key, val in person.items():
    print(key, val)

person.update({"age": 26, "job": "dev"})
person.pop("job")      # remove & return

# Set
s = {1, 2, 3, 2}      # {1, 2, 3}
s.add(4); s.remove(2)
s1 | s2                # union
s1 & s2                # intersection
s1 - s2                # difference

# List comprehension
squares = [x**2 for x in range(10)]
evens   = [x for x in range(20) if x % 2 == 0]
flat    = [x for row in matrix for x in row]

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

# Set comprehension
unique_sq = {x**2 for x in [-1, 0, 1, 2, 2]}

# Generator expression (lazy, memory-efficient)
total = sum(x**2 for x in range(1000))

# Conditional in value
labels = ["even" if x%2==0 else "odd" for x in range(5)]

class Animal:
    # Class variable
    kingdom = "Animalia"

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

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

    def __str__(self):
        return f"Animal({self.name}, {self.age})"

    @classmethod
    def create(cls, name):
        return cls(name, 0)

    @staticmethod
    def is_animal(x):
        return isinstance(x, Animal)

class Dog(Animal):  # inheritance
    def speak(self):
        return f"{self.name} barks!"

d = Dog("Rex", 3)
print(d.speak())
print(isinstance(d, Animal))  # True

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

for line in open("file.txt"):
    print(line.strip())

# Write file
with open("output.txt", "w") as f:
    f.write("Hello\n")
    f.writelines(["line1\n","line2\n"])

# Append
with open("log.txt", "a") as f:
    f.write("new entry\n")

# JSON
import json
data = json.loads('{"key":"val"}')  # parse
text = json.dumps(data, indent=2)  # stringify
with open("data.json","w") as f:
    json.dump(data, f, indent=2)

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

# Raise exceptions
raise ValueError("Invalid input")
raise TypeError(f"Expected int, got {type(x)}")

# Custom exception
class MyError(Exception):
    pass

raise MyError("Something went wrong")

len([1,2,3])        # 3
range(5)            # 0-4
range(1, 10, 2)     # 1,3,5,7,9
enumerate(lst)      # (index, value) pairs
zip(a, b)           # pair elements
map(fn, lst)        # apply fn to each
filter(fn, lst)     # filter by fn
sorted(lst, key=..., reverse=True)
all([True,True])    # True
any([False,True])   # True
sum([1,2,3])        # 6
min([3,1,2])        # 1
max([3,1,2])        # 3
abs(-5)             # 5
round(3.7)          # 4
print(f"{val:.2f}") # format float
hex(255)            # "0xff"
bin(10)             # "0b1010"
input("Enter: ")    # user input