Python Programming
Complete Notes

# This is a comment - Python ignores this line
print("Hello, World!")

# Output:
# Hello, World!

python filename.py
# or on some systems:
python3 filename.py

name = "Ali"        # string
age = 20            # integer
gpa = 3.75          # float
is_pass = True      # boolean

x = 25
y = 3.14
z = "Python"

print(type(x))   # <class 'int'>
print(type(y))   # <class 'float'>
print(type(z))   # <class 'str'>

age = "20"             # string
age = int(age)         # now an integer
print(age + 5)         # 25

price = 99
price_text = str(price)
print("Price: " + price_text)   # Price: 99

result = 5 + 3 * 2      # Multiplication happens first
print(result)             # 11

result = (5 + 3) * 2     # Parentheses happen first
print(result)             # 16

print("Hello", "World")                 # Hello World
print("Hello", "World", sep="-")        # Hello-World
print("Hello", end=" ")
print("World")                          # Hello World (same line)

name = input("Enter your name: ")
age = int(input("Enter your age: "))
print(name, "is", age, "years old")

name = "Ayesha"
gpa = 3.85
print(f"Student: {name}, GPA: {gpa:.1f}")
# Output: Student: Ayesha, GPA: 3.9

marks = 85
if marks >= 50:
    print("You passed!")

marks = 35
if marks >= 50:
    print("You passed!")
else:
    print("You failed.")

marks = 72
if marks >= 90:
    grade = "A"
elif marks >= 80:
    grade = "B"
elif marks >= 70:
    grade = "C"
else:
    grade = "F"
print("Grade:", grade)

age = 20
has_id = True
if age >= 18:
    if has_id:
        print("Entry allowed")
    else:
        print("ID required")
else:
    print("Too young to enter")

age = 17
status = "Adult" if age >= 18 else "Minor"
print(status)     # Minor

for i in range(1, 6):
    print(i)
# Output: 1 2 3 4 5 (each on a new line)

count = 1
while count <= 5:
    print(count)
    count += 1

for i in range(1, 10):
    if i == 5:
        break          # stop loop completely
    if i % 2 == 0:
        continue        # skip even numbers
    print(i)
# Output: 1 3

# Print a triangle pattern
for i in range(1, 5):
    for j in range(i):
        print("*", end="")
    print()
# Output:
# *
# **
# ***
# ****

s1 = 'Hello'
s2 = "World"
s3 = '''This is a
multi-line string'''

word = "Python"
print(word[0])      # P (first character)
print(word[-1])     # n (last character)
print(word[0:4])    # Pyth (index 0 to 3)
print(word[2:])     # thon (index 2 to end)
print(word[::-1])   # nohtyP (reversed string)

first = "Pak"
last = "Notes"
print(first + last)      # PakNotes  (concatenation)
print(first * 3)          # PakPakPak (repetition)

fruits = ["apple", "banana", "cherry"]
mixed = [1, "two", 3.0, True]
print(fruits[0])        # apple
fruits.append("mango")  # add an item
fruits[1] = "grapes"    # update an item
print(fruits)

numbers = [10, 20, 30, 40, 50]
print(numbers[1:4])     # [20, 30, 40]
print(numbers[:3])      # [10, 20, 30]
print(numbers[::2])     # [10, 30, 50] (every 2nd item)

squares = [x**2 for x in range(1, 6)]
print(squares)             # [1, 4, 9, 16, 25]

evens = [x for x in range(1, 11) if x % 2 == 0]
print(evens)                # [2, 4, 6, 8, 10]

point = (10, 20)
print(point[0])      # 10
# point[0] = 5       # Error! Tuples cannot be modified

point = (10, 20)
x, y = point          # unpacking
print(x, y)             # 10 20

a, b, c = 1, 2, 3      # packing into separate variables

student = {"name": "Ali", "age": 20, "gpa": 3.7}
print(student["name"])       # Ali
student["age"] = 21            # update value
student["dept"] = "CS"         # add new key

student = {"name": "Ali", "age": 20, "gpa": 3.7}
for key, value in student.items():
    print(key, "->", value)

nums = {1, 2, 2, 3, 3, 3}
print(nums)             # {1, 2, 3} — duplicates removed
nums.add(4)
nums.remove(1)

a = {1, 2, 3}
b = {2, 3, 4}
print(a | b)    # {1, 2, 3, 4}  union
print(a & b)    # {2, 3}        intersection
print(a - b)    # {1}           difference

def greet(name):
    print(f"Hello, {name}!")

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

def add(a, b=10):              # b has a default value
    return a + b

print(add(5))            # 15 (uses default b=10)
print(add(5, 20))        # 25
print(add(a=5, b=2))     # 7 (keyword arguments)

def total(*args):
    return sum(args)
print(total(1, 2, 3, 4))     # 10

def show_info(**kwargs):
    for key, value in kwargs.items():
        print(key, ":", value)
show_info(name="Ali", age=20)

def square(n):
    return n * n

result = square(5)
print(result)     # 25

x = 10            # global variable
def show():
    x = 5           # local variable (different from global x)
    print("Inside:", x)
show()               # Inside: 5
print("Outside:", x) # Outside: 10

def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n - 1)

print(factorial(5))    # 120

square = lambda x: x * x
print(square(5))         # 25

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

numbers = [1, 2, 3, 4]
squares = list(map(lambda x: x**2, numbers))
print(squares)           # [1, 4, 9, 16]

numbers = [1, 2, 3, 4, 5, 6]
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(evens)             # [2, 4, 6]

from functools import reduce
numbers = [1, 2, 3, 4]
product = reduce(lambda a, b: a * b, numbers)
print(product)            # 24

squares_dict = {x: x**2 for x in range(1, 5)}
print(squares_dict)    # {1: 1, 2: 4, 3: 9, 4: 16}

print(10 / 0)
# Output: ZeroDivisionError: division by zero

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(result)
except ZeroDivisionError:
    print("You cannot divide by zero!")
except ValueError:
    print("Please enter a valid number!")

try:
    x = int("10")
except ValueError:
    print("Invalid input")
else:
    print("No errors:", x)
finally:
    print("Execution finished")

def set_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    return age

set_age(-5)    # raises ValueError

class InsufficientBalanceError(Exception):
    pass

def withdraw(balance, amount):
    if amount > balance:
        raise InsufficientBalanceError("Not enough balance!")
    return balance - amount

file = open("notes.txt", "r")     # open for reading
content = file.read()
file.close()                        # always close the file

with open("notes.txt", "r") as file:
    for line in file:
        print(line.strip())

with open("notes.txt", "w") as file:
    file.write("Pak Notes Hub\n")
    file.write("Python Programming Course\n")

with open("notes.txt", "a") as file:
    file.write("Added later using append mode\n")

class Student:
    def __init__(self, name, roll_no):
        self.name = name
        self.roll_no = roll_no

    def display(self):
        print(f"{self.roll_no} - {self.name}")

s1 = Student("Ali", 101)
s1.display()           # 101 - Ali

class Person:
    def __init__(self, name):
        self.name = name
    def show(self):
        print("Name:", self.name)

class Student(Person):            # Student inherits from Person
    def __init__(self, name, roll_no):
        super().__init__(name)     # call parent constructor
        self.roll_no = roll_no

s = Student("Sara", 12)
s.show()                # Name: Sara

class Cat:
    def sound(self):
        print("Meow")

class Dog:
    def sound(self):
        print("Woof")

for animal in [Cat(), Dog()]:
    animal.sound()        # Meow, then Woof

class Account:
    def __init__(self, balance):
        self.__balance = balance      # private attribute

    def deposit(self, amount):
        self.__balance += amount

    def get_balance(self):
        return self.__balance

import math
print(math.sqrt(25))      # 5.0
print(math.pi)              # 3.141592653589793

from random import randint
print(randint(1, 10))      # random number between 1 and 10

# mymath.py
def add(a, b):
    return a + b

# main.py
import mymath
print(mymath.add(3, 4))     # 7

pip install numpy
pip install pandas
pip list                     # shows installed packages

tasks = []

def show_menu():
    print("\n--- TO-DO LIST ---")
    print("1. Add Task")
    print("2. View Tasks")
    print("3. Remove Task")
    print("4. Exit")

def add_task():
    task = input("Enter task: ")
    tasks.append(task)
    print("Task added!")

def view_tasks():
    if not tasks:
        print("No tasks yet.")
    for i, task in enumerate(tasks, start=1):
        print(f"{i}. {task}")

def remove_task():
    view_tasks()
    try:
        num = int(input("Enter task number to remove: "))
        tasks.pop(num - 1)
        print("Task removed!")
    except (ValueError, IndexError):
        print("Invalid task number.")

while True:
    show_menu()
    choice = input("Choose an option: ")
    if choice == "1":
        add_task()
    elif choice == "2":
        view_tasks()
    elif choice == "3":
        remove_task()
    elif choice == "4":
        print("Goodbye!")
        break
    else:
        print("Invalid choice, try again.")