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

# One-liner (ternary)
label = "Adult" if age >= 18 else "Minor"

# Nested conditions
if score >= 90 and attendance >= 80:
    grade = "A"
elif score >= 70 or bonus_marks:
    grade = "B"

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

for i in range(1, 11, 2):   # 1,3,5,7,9 (start,stop,step)
    print(i)

# for loop — iterate over list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# enumerate — get index AND value
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

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

# break and continue
for n in range(10):
    if n == 5: break      # exit loop
    if n % 2 == 0: continue  # skip to next
    print(n)               # prints 1, 3

# Basic function
def greet(name):
    return f"Hello, {name}!"

print(greet("Ahmed"))   # Hello, Ahmed!

# Default parameters
def power(base, exp=2):
    return base ** exp

power(3)       # 9 (uses default exp=2)
power(3, 3)    # 27

# *args — variable number of arguments
def total(*numbers):
    return sum(numbers)

total(1, 2, 3, 4)  # 10

# **kwargs — keyword arguments
def profile(**info):
    for key, val in info.items():
        print(f"{key}: {val}")

profile(name="Ahmed", age=17, city="Lahore")

# Lambda (anonymous function)
square = lambda x: x ** 2
print(square(5))   # 25

add = lambda a, b: a + b
print(add(3, 4))   # 7

# Multiple return values
def min_max(lst):
    return min(lst), max(lst)

lo, hi = min_max([3, 1, 7, 2])  # lo=1, hi=7

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

# Indexing & slicing
nums[0]         # 3  (first)
nums[-1]        # 9  (last)
nums[1:4]       # [1, 4, 1]  (slice)
nums[::-1]      # [9,5,1,4,1,3]  (reverse)

# Methods
nums.append(2)       # add to end
nums.insert(0, 10)  # insert at index
nums.remove(1)       # remove first occurrence
nums.pop()            # remove and return last
nums.pop(2)          # remove at index 2
nums.sort()           # sort in-place
nums.sort(reverse=True)  # sort descending
nums.reverse()        # reverse in-place
nums.count(1)        # count occurrences
nums.index(5)        # find index of value
len(nums)             # length

# Useful built-ins
sorted(nums)          # return sorted copy
sum(nums)             # sum all elements
min(nums), max(nums)  # min and max
list(set(nums))       # remove duplicates

# List comprehension
squares = [x**2 for x in nums]
big = [x for x in nums if x > 3]

student = {"name": "Ahmed", "age": 17, "gpa": 3.8}

# Access
student["name"]              # "Ahmed"
student.get("grade", "N/A") # safe access with default

# Modify
student["age"] = 18          # update value
student["city"] = "Lahore"   # add new key
del student["gpa"]           # delete key

# Iterate
for key in student:                 # keys
    print(key)
for val in student.values():       # values
    print(val)
for k, v in student.items():      # both
    print(f"{k}: {v}")

# Methods
student.keys()    # dict_keys([...])
student.values()  # dict_values([...])
student.pop("age")       # remove & return
student.update({"score": 95})  # merge/update
in student                 # check key exists

# Sets — unique unordered elements
a = {1, 2, 3, 4}
b = {3, 4, 5, 6}
a | b    # union    {1,2,3,4,5,6}
a & b    # intersection {3,4}
a - b    # difference   {1,2}
a.add(10)    # add element
a.remove(1) # remove element

s = "  Hello, World!  "

# Case
s.upper()        # "  HELLO, WORLD!  "
s.lower()        # "  hello, world!  "
s.title()        # "  Hello, World!  "

# Strip whitespace
s.strip()        # "Hello, World!"
s.lstrip()       # "Hello, World!  " (left only)
s.rstrip()       # "  Hello, World!" (right only)

# Search
s.find("World")  # 9 (index) or -1 if not found
s.count("l")    # 3
"Hello" in s    # True
s.startswith("  H")  # True
s.endswith("  ")    # True

# Modify
s.replace("World", "Python")   # replace
", ".join(["a", "b", "c"])     # "a, b, c"
s.split(",")                   # ["  Hello", " World!  "]

# Format
f"Name: {name}, Age: {age}"   # f-string (Python 3.6+)
f"Pi = {3.14159:.2f}"         # "Pi = 3.14"
f"{1000000:,}"                 # "1,000,000"
f"{0.75:.0%}"                  # "75%"

# Slicing strings
word = "Python"
word[0]      # "P"
word[-1]     # "n"
word[2:5]    # "tho"
word[::-1]   # "nohtyP" (reverse)

class Animal:
    # Class variable (shared by all instances)
    species_count = 0

    def __init__(self, name, sound):
        # Instance variables
        self.name = name
        self.sound = sound
        Animal.species_count += 1

    def speak(self):
        return f"{self.name} says {self.sound}!"

    def __str__(self):               # for print()
        return f"Animal: {self.name}"

    def __repr__(self):              # for debugging
        return f"Animal('{self.name}')"

# Create objects
dog = Animal("Dog", "Woof")
cat = Animal("Cat", "Meow")
print(dog.speak())   # Dog says Woof!

# Inheritance
class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name, "Woof")  # call parent __init__
        self.breed = breed

    def fetch(self):                 # new method
        return f"{self.name} fetches the ball!"

    def speak(self):                 # override parent method
        return f"{self.name} barks loudly!"

rex = Dog("Rex", "German Shepherd")
print(rex.speak())   # Rex barks loudly!
print(rex.fetch())   # Rex fetches the ball!
isinstance(rex, Animal)  # True

# Writing a file
with open("data.txt", "w") as f:
    f.write("Hello, File!\n")
    f.write("Second line\n")

# Reading a file — full content
with open("data.txt", "r") as f:
    content = f.read()
    print(content)

# Reading line by line
with open("data.txt", "r") as f:
    for line in f:
        print(line.strip())

# Read all lines as list
with open("data.txt") as f:
    lines = f.readlines()   # ['Hello, File!\n', ...]

# Append to file
with open("data.txt", "a") as f:
    f.write("Appended line\n")

# File modes: "r" read, "w" write, "a" append, "rb" binary

try:
    num = int(input("Enter a number: "))
    result = 100 / num
    print(f"Result: {result}")
except ValueError:
    print("Error: Please enter a valid number")
except ZeroDivisionError:
    print("Error: Cannot divide by zero")
except Exception as e:
    print(f"Unexpected error: {e}")
else:
    print("No error occurred!")   # runs if no exception
finally:
    print("This always runs")       # cleanup code

# Raise your own exceptions
def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    return age

import math
math.sqrt(16)      # 4.0
math.pi             # 3.14159…
math.ceil(3.2)    # 4
math.floor(3.8)   # 3

import random
random.random()             # 0.0 to 1.0
random.randint(1, 6)       # dice roll 1-6
random.choice(["a","b","c"])  # random pick
random.shuffle(my_list)     # shuffle in-place

import datetime
now = datetime.datetime.now()
print(now.strftime("%Y-%m-%d %H:%M"))

from collections import Counter, defaultdict
word_count = Counter(["a","b","a","c","a"])
# Counter({'a': 3, 'b': 1, 'c': 1})

# os module
import os
os.getcwd()          # current directory
os.listdir(".")     # list files
os.path.exists("file.txt")  # check if exists