Lesson 2: Python Basics: Variables se Strings tak

Arre waah bro, welcome back to my blog! Main hoon aapka bhaiya, ek senior Python developer jo ab blogging kar raha hai. Aaj hum baat karenge Python ke fundamentals pe – variables, data types, operators, aur phir input-output with strings. Kyun? Kyunki ye sab basics hain yaar, bina inke aage badh nahi sakte. Imagine karo tu ek naya developer hai, code likh raha hai aur suddenly error aa jaata hai kyunki variable ka type galat hai. Been there done that! Mujhe yaad hai jab main college mein tha pehla Python script likha, socha sab easy hai... lekin phir operators mix up kar diye aur program infinite loop mein phas gaya. Has has ke pet dukha tha us din!

Bro ye article tere jaise juniors ke liye hai – casual, fun, thoda hinglish mein taaki lage jaise main personally baat kar raha hoon. Hum step by step jayenge stories sunayenge jokes marenge aur end mein ek mini project bhi karenge. Ready ho? Chalo shuru karte hain. Coffee le lo long read hai ye!

Variables, Constants aur Naming Rules – Foundation Hai Ye

Variables? Ek box jisme tu data rakhta hai, jaise dabba mein biryani. Python mein bas likh: naam = value. No need to declare type, Python khud samajh leta hai.

Constants? Fixed values, jaise math ka PI. Python mein true constant nahi, lekin uppercase naam rakho (convention), taaki sabko pata chale change nahi karna.

Naming rules zaroori hain, warna errors! Yahaan quick table:

Rule	Valid Example	Invalid Example
Start with letter or _	score, _count	1score
Only letters, numbers, _	user_age2	user@name
Case sensitive	Age != age	N/A
No reserved words	my_loop	for
Use snake_case	total_marks	totalMarks

Code dekho:

PI = 3.14159  # Constant
user_age = 25  # Variable

Story: Ek baar maine variable 'x' rakha, project bada hua, aur bhool gaya x kya tha. Debugging mein dimag kharab! Hamesha descriptive naam rakh, bro!

Common galti: Invalid names ya reserved words. Fix: Naam badlo, snake_case use karo.

Data Types – Kya Kya Store Kar Sakte Ho?

Data types batate hain variable mein kya hai. Python ke main types:

Type	Description	Example
int	Whole numbers	42, -100
float	Decimals	3.14, 2.5e3
str	Text	"Hello", 'Bro'
bool	True/False	True, False
complex	Complex numbers	2+3j

Type check karne ka tareeka:

print(type(42))  # <class 'int'>
print(type("Bro"))  # <class 'str'>

Python dynamic typed hai – type change ho sakta hai, jaise user_age = 25; user_age = "twenty five". Flexible, lekin bugs se bacho!

Type Conversion & Casting – Data Ko Transform Karo

Kabhi string ko number chahiye? Use int(), float(), str(), bool().

Misal:

str_num = "123"
int_num = int(str_num)  # 123
float_num = float("3.14")  # 3.14

Implicit conversion: 1 + 2.0 = 3.0 (float). Explicit safe hai.

Galti: int("abc") – ValueError. Fix: Try-except (baad mein sikhenge).

Kyun zaroori? User input, APIs – sab mixed data dete hain.

Operators – Code Ka Masala

Operators ka full breakdown with tables. Categories: Arithmetic, Comparison, Logical, Assignment, Bitwise.

Arithmetic Operators

Operator	Description	Example	Result
+	Addition	5 + 3	8
-	Subtraction	5 - 3	2
*	Multiplication	5 * 3	15
/	Division	5 / 2	2.5
//	Floor Division	5 // 2	2
%	Modulo	5 % 2	1
**	Exponent	5 ** 2	25

Comparison Operators

Operator	Description	Example	Result
==	Equal	5 == 5	True
!=	Not Equal	5 != 3	True
>	Greater Than	5 > 3	True
<	Less Than	5 < 3	False
>=	Greater or Equal	5 >= 5	True
<=	Less or Equal	5 <= 3	False

Logical Operators

Operator	Description	Example	Result
and	Both True	True and False	False
or	Any True	True or False	True
not	Invert	not True	False

Assignment Operators

Operator	Example	Equivalent
=	x = 5	x = 5
+=	x += 3	x = x + 3
-=	x -= 3	x = x - 3
*=	x *= 3	x = x * 3
/=	x /= 3	x = x / 3

Bitwise Operators

Binary level pe: & (AND), | (OR), ^ (XOR), ~ (NOT), << (Left Shift), >> (Right Shift).

a = 5  # 101
b = 3  # 011
print(a & b)  # 1 (001)

Operator Precedence Chart

Kaun pehle? Yahaan table:

Precedence (High to Low)	Operators
1	**
2	~ + - (unary)
3	* / // %
4	+ -
5	<< >>
6	&
7	^ |
8	== != > < >= <=
9	not
10	and
11	or

Joke: Precedence na samjha to code jaise traffic jam! Parentheses () use karo clarity ke liye.

Galti: 2 + 3 * 4 = 14 (not 20). Precedence yaad rakh!

Mini Practice Exercises – Ab Tu Try Kar

Practice se perfect banoge:

• Constant GRAVITY = 9.8, print karo.
• Check type of 3.14 aur "3.14".
• "45.67" ko float, +10 karo.
• Calculate 10 ** 2 % 3, precedence dhyan se.
• Logical: If (age > 18 and score >= 80), print "Pass".

Run karo, galti se seekho. Pehli baar modulo samajh nahi aaya, game score mein use kiya tab clear hua!

Taking Input from Users – Program Ko Interactive Banao

input() string deta hai. Numbers ke liye convert.

age = int(input("Age bata bro: "))

Galti: Convert bhoolna ya invalid input. Fix: Validate karo, spaces ke liye strip().

Formatting Output – Output Ko Cool Banao

f-strings sabse best (Python 3.6+).

name = "Raj"
age = 22
print(f"Yo {name}, tu {age} ka hai!")

Alternative: .format(), lekin f-strings fast. Old % ab mat use.

Strings in Depth – Text Ka Khel

Indexing: s[0] first char. Slicing: s[start:end:step].

s = "PythonBro"
print(s[0:6])  # Python
print(s[::-1])  # orByhtyp

ASCII chart for clarity:

P y t h o n B r o
0 1 2 3 4 5 6 7 8
-9-8-7-6-5-4-3-2-1

Concat: s1 + s2. Strings immutable – change ke liye new string.

String Methods – Super Toolkit

Method	Description	Example	Result
upper()	Uppercase	"bro".upper()	"BRO"
lower()	Lowercase	"BRO".lower()	"bro"
replace(old, new)	Replace	"hi bro".replace("bro", "dude")	"hi dude"
split(sep)	Split to list	"a b c".split()	['a', 'b', 'c']
join(list)	Join list	" ".join(['a', 'b'])	"a b"
strip()	Remove spaces	" bro ".strip()	"bro"
find(sub)	Find index	"bro".find("r")	1
count(sub)	Count	"bro bro".count("bro")	2

Story: Ek app mein usernames clean kiye strip() aur lower() se, duplicates gone!

Hands-on Project: Basic Username Formatter

Chalo, ek project: User se naam lo, lowercase karo, spaces hatao, aur end mein "007" add karo.

1. Input full name
2. Lowercase
3. Remove spaces
4. Add "007"
5. Print username

full_name = input("Naam daal bro: ")
clean_name = full_name.lower().replace(" ", "")
username = clean_name + "007"
print(f"Tera username: {username}")

Extend: Check if name empty, print "Kuch daal!"

Conclusion – Tu Ab Pro Hai!

Bro, full lesson khatam! Variables se strings, tables, charts, sab cover kiya. Practice kar, galtiyan kar, seekh. Next: Loops aur if-else. Comment mein bata kaisa laga, subscribe kar! Coding masti hai, stress mat le! 😎