BASIC PYTHON

🐍 Python – Complete Basic Notes

Syntax, Variables, Data Types, Operators, Conditionals, Loops, Functions aur Collections ka complete quick guide.

1️⃣ Python Kya Hai?

Definition: Python ek high-level, general-purpose aur beginner-friendly programming language hai jise padhna aur likhna English jaisa aasan hota hai.

Kyun Seekhein: Python ka syntax bohot concise hota hai. Jis kaam ke liye C ya Java me 10 lines likhni padti hain, Python me wahi kaam sirf 1-2 lines me ho jata hai.

• Readable Syntax: Complex symbols (jaise {} ya ;) ki jagah clean indentation (spaces) use karta hai.
• Interpreted: Code line-by-line execute hota hai, isliye errors jaldi pakad me aate hain.
• Industry Use: Backend Web Development, Artificial Intelligence (AI), Machine Learning (ML), Data Analysis aur Automation me sabse zyada popular.

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2️⃣ Python Ke Core Features

• Simple & Easy: Beginners ke coding shuru karne ke liye best language.
• Dynamically Typed: Variables ka data type manually declare nahi karna padta, Python value dekh kar khud decide kar leta hai.
• Rich Standard Library: Har task ke liye hazaron ready-made packages aur built-in modules available hain.
• Cross-Platform: Windows, macOS aur Linux par bina change kiye same run hota hai.

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3️⃣ First Python Program

Ek file banayein app.py aur usme yeh line likhein:

print("Hello Python World!")

Terminal me run karne ke liye likhein:

python app.py

Live Python Execution Simulation

$ Click the button above to simulate running python code...

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4️⃣ Variables & Data Types

Python me variable declare karne ke liye koi keyword (jaise var ya int) nahi lagta:

name = "Rahul"        # str (Text)
age = 20              # int (Whole Number)
height = 5.7          # float (Decimal Number)
is_student = True     # bool (True ya False)

Data Type	Example	Description
str	"Python", 'Code'	Text characters enclosed in quotes
int	10, -45, 1000	Bina decimal wale positive ya negative numbers
float	3.14, -0.5	Decimal fraction wale numbers
bool	True, False	Logical state (Pehla letter Capital hota hai)

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5️⃣ Operators

Values aur variables par calculation ya logic execute karne ke symbols:

Type	Symbols	Example	Meaning
Arithmetic	+, -, *, /, %	10 % 3	Modulus (Remainder = 1)
Assignment	=, +=, -=, *=	x += 5	Same as x = x + 5
Comparison	==, !=, >, <, >=	age >= 18	Result True ya False deta hai
Logical	and, or, not	x > 5 and y < 10	English words use karta hai (No && or ||)

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6️⃣ Conditionals (if, elif, else)

Decisions lene ke liye Python Indentation (4 spaces) use karta hai curly brackets {} ki jagah:

age = 20

if age >= 18:
    print("Eligible to Vote (Adult)")
elif age >= 13:
    print("Teenager")
else:
    print("Minor")

Indentation Rule: if ya colon : ke baad aane wali lines ko thoda aage (space dekar) likhna mandatory hai. Agar indentation galat hua toh Python IndentationError dega.

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7️⃣ Loops (Code Repetition)

1. For Loop (range function ke sath)

# 1 se lekar 5 tak print karega (6 exclude rehta hai)
for i in range(1, 6):
    print("Count:", i)

2. While Loop (Condition check ke sath)

i = 1
while i <= 5:
    print("Iteration:", i)
    i += 1  # Increment lazmi hai infinite loop se bachne ke liye

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8️⃣ Functions

Definition: Reusable code block jise def keyword se define kiya jata hai.

# Function Definition
def greet(name):
    return "Hello, " + name + "!"

# Function Call
msg = greet("Rahul")
print(msg)  # "Hello, Rahul!"

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9️⃣ Lists & Dictionaries (Core Collections)

1. List (Ordered, Changeable Collection)

fruits = ["Apple", "Banana", "Mango"]
print(fruits[0])       # "Apple" (First item)
fruits.append("Orange") # Element add karta hai
print(len(fruits))     # Total length

2. Dictionary (Key-Value Pairs)

person = {
    "name": "Rahul",
    "age": 20,
    "city": "Indore"
}

print(person["name"])  # "Rahul"
person["age"] = 21     # Value update karna

Collection	Syntax	Access Pattern
List	Square Brackets []	Index number se: list[0]
Dictionary	Curly Brackets {}	Key ke naam se: dict["key"]