1. Variables in Python
Variable ek container jaisa hota hai jisme hum koi value store karte hain.
Rules of Writing Variables:
- Variable ka naam letter ya underscore (_) se start hona chahiye
- Kabhi bhi number se start mat karo (❌ 2name = "abc")
- No special characters allowed (❌ name$ = "abc")
- Spaces nahi aani chahiye (❌ my name = "abc")
- Python ke keywords (if, else, class) ka use variable naam ke liye mat karo
✅ Right Way:
name = "Amit"
age = 25
❌ Wrong Way:
2name = "Amit" # ❌ Invalid: number se start nahi ho sakta
my name = "Amit" # ❌ Invalid: spaces not allowed
class = "ABC" # ❌ Invalid: 'class' is a keyword
Output:
Amit
25
2. Input from User
input() function user se data lene ke liye use hota hai. By default yeh string deta hai.
name = input("Enter your name: ")
print("Welcome", name)
Enter your name: Ravi
Welcome Ravi
Common Mistake:
age = input("Enter age: ")
print(age + 5) # ❌ Error: string + int not allowed
Correct Way:
age = int(input("Enter age: "))
print(age + 5)
Enter age: 20
25
3. Data Types in Python
- int: Integer values jaise 1, 100, -5
- float: Decimal values jaise 3.14, -0.5
- str: Text ya characters, like "Hello"
- bool: True ya False (boolean)
- complex: Complex numbers like 2 + 3j
a = 5
b = 3.14
c = "Hi"
d = True
e = 4 + 2j
print(type(a), type(b), type(c), type(d), type(e))
<class 'int'> <class 'float'> <class 'str'> <class 'bool'> <class 'complex'>
4. Type Casting
Type casting matlab ek data type ko dusre me badalna.
✅ Right Example:
num = "10"
num = int(num)
print(num + 5)
15
❌ Wrong Example:
num = "ten"
num = int(num) # ❌ Error: 'ten' string ko int me convert nahi kar sakte
5. print() Function
print() ka use output dikhane ke liye hota hai. Kuch bhi show karna ho screen pe, print ka use hota hai.
print("Learning Python is fun!")
Learning Python is fun!