Python Fundamentals

# Python mein Hello World — sirf 1 line!
print("Hello, World!")

# C++ mein same kaam — 5 lines!
# #include <iostream>
# using namespace std;
# int main() {
#     cout << "Hello, World!";
#     return 0;
# }

python --version\n# Output: Python 3.12.x

>>> print("Hello, World!")
Hello, World!

>>> 2 + 3
5

>>> name = "Python"
>>> print(f"I love {name}!")
I love Python!

>>> exit()  # Interactive mode se bahar aane ke liye

# hello.py file banao aur ye likho:
print("Namaste! Mera naam Python hai!")
print("Mein ek programming language hoon.")

for i in range(1, 6):
    print(f"Counting: {i}")

# calculator.py - ek simple calculator
num1 = 10
num2 = 5

print(f"Jod (Sum): {num1 + num2}")      # 15
print(f"Ghata (Diff): {num1 - num2}")    # 5
print(f"Guna (Multiply): {num1 * num2}") # 50
print(f"Bhaag (Divide): {num1 / num2}")  # 2.0

# ✅ Sahi (Valid) Identifiers:
name = "Rahul"
student_1 = "Priya"
_private = "Secret"
totalMarks = 450

# ❌ Galat (Invalid) Identifiers:
# 123name = "Error"    → Number se shuru nahi ho sakta
# my-var = 10          → Hyphen (-) allowed nahi
# for = 5             → Reserved keyword hai
# $price = 100        → Special symbol nahi chalega

# Keywords check karne ka tarika:
import keyword
print(keyword.kwlist)
print(f"Total keywords: {len(keyword.kwlist)}")

# Single quotes
name = 'Rahul'

# Double quotes
city = "Delhi"

# Triple quotes - jab text multiple lines mein ho
poem = """Twinkle twinkle little star,
How I wonder what you are.
Up above the world so high,
Like a diamond in the sky."""

print(poem)

# Integer (poore numbers)
age = 18
marks = 95

# Float (decimal wale numbers)
height = 5.8
pi = 3.14159

# Binary (0b se shuru)
binary = 0b1010  # ye hai 10

# Hexadecimal (0x se shuru)
hex_num = 0xFF   # ye hai 255

print(f"Age: {age}, Height: {height}")
print(f"Binary 0b1010 = {binary}")  # Output: 10

# Boolean - True ya False
is_student = True
has_passed = False
print(is_student)  # True

# None - koi value nahi
result = None
print(result)      # None
print(type(result)) # <class 'NoneType'>

# Variable banane ka tarika: naam = value
name = "Rahul"        # String (text)
age = 18              # Integer (poora number)
height = 5.8          # Float (decimal number)
is_student = True     # Boolean (haan/nahi)
fav_fruits = ["Apple", "Mango"]  # List

# Type check karo - Python khud batata hai!
print(type(name))      # <class 'str'>
print(type(age))       # <class 'int'>
print(type(height))    # <class 'float'>
print(type(is_student)) # <class 'bool'>

# Variable ki value change bhi kar sakte ho!
age = 19  # ab age 19 hai
print(f"{name} ki age {age} hai aur height {height} hai")

a = 10
b = 3
print(f"Jod: {a + b}")        # 13
print(f"Ghatao: {a - b}")     # 7
print(f"Guna: {a * b}")       # 30
print(f"Bhaag: {a / b}")      # 3.333...
print(f"Floor: {a // b}")     # 3 (decimal hata do)
print(f"Remainder: {a % b}")  # 1
print(f"Power: {a ** b}")     # 1000

x = 5
y = 10

print(x == y)   # False (5 barabar 10? Nahi!)
print(x != y)   # True  (5 alag hai 10 se? Haan!)
print(x > y)    # False (5 bada hai 10 se? Nahi!)
print(x < y)    # True  (5 chhota hai 10 se? Haan!)
print(x >= 5)   # True  (5 barabar ya bada 5 se? Haan!)
print(x <= 3)   # False (5 barabar ya chhota 3 se? Nahi!)

a = [1, 2, 3]
b = [1, 2, 3]  # Same value, but different object!
c = a          # Same object

print(a == b)   # True  (values same hain)
print(a is b)   # False (objects alag hain)
print(a is c)   # True  (c toh a ka hi naam hai!)

fruits = ["apple", "banana", "mango"]

print("banana" in fruits)     # True  ✅ hai!
print("grape" in fruits)      # False ❌ nahi hai!
print("grape" not in fruits)  # True  ✅ sahi, nahi hai!

# Strings mein bhi kaam karta hai:
print("py" in "python")       # True ✅

# Colon (:) - function definition mein
def namaste(name):     # ← colon yahan hai
    print(f"Namaste, {name}!")

# Brackets - list banao
fruits = ["Apple", "Banana", "Mango"]  # ← square brackets

# Curly braces - dictionary banao
student = {"name": "Rahul", "age": 18}  # ← curly braces

# Hash (#) - comments likhne ke liye
# Ye line Python ignore karega

print("Hello, World!")       # Text print karo
print(42)                   # Number print karo
print(True)                 # Boolean print karo
print("Mera naam", "Rahul") # Multiple items print karo
# Output: Mera naam Rahul

# sep = items ke beech mein kya aaye
print("Apple", "Banana", "Mango", sep=" | ")
# Output: Apple | Banana | Mango

# end = line ke end mein kya aaye (default: new line)
print("Hello", end=" ")
print("World!")
# Output: Hello World!  (ek hi line mein!)

name = "Rahul"
age = 18
marks = 95.5

# f-string: f"..." ke andar {variable} likho
print(f"Mera naam {name} hai")
print(f"Meri age {age} hai")
print(f"Mere marks {marks} hain")
print(f"Next year meri age {age + 1} hogi")

# Old tarika (format method)
print("Naam: {}, Age: {}".format(name, age))

# User se naam pucho
name = input("Aapka naam kya hai? ")
print(f"Namaste, {name}! Kaise ho?")

# Output:
# Aapka naam kya hai? Rahul  ← user type karega
# Namaste, Rahul! Kaise ho?

# ⚠️ input() hamesha STRING deta hai!
age_str = input("Age batao: ")  # ye string hai: "18"
age = int(age_str)              # ab integer hai: 18

# Short tarika — ek hi line mein:
age = int(input("Age batao: "))
next_year = age + 1
print(f"Next year aap {next_year} saal ke ho jaoge!")

# Float ke liye
height = float(input("Height batao (meters): "))
print(f"Aapki height {height} meters hai")

# Ek line mein do numbers lo
x, y = input("Do numbers likho (space se alag): ").split()
x, y = int(x), int(y)

print(f"Jod: {x + y}")
print(f"Guna: {x * y}")

name = "Knobly Web"

# Length (kitne characters hain)
print(len(name))          # 9

# Uppercase / Lowercase
print(name.upper())       # Knobly Web
print(name.lower())       # Knobly Web

# Slicing (hissa nikalo)
print(name[0:6])          # Knobly (index 0 se 5 tak)
print(name[-2:])          # OS (last 2 characters)

# Replace (badal do)
print(name.replace("OS", "System"))  # Knobly System

# Check karo kuch hai ya nahi
print("Knobly" in name)   # True ✅
print("Python" in name)   # False ❌

# Split (tod do)
words = "apple,banana,mango".split(",")
print(words)  # ['apple', 'banana', 'mango']