Python Variables

byMy Scribble Pads •August 11, 2025

Python Variables

1. What is a Variable?

A variable is a named location in memory that stores data.
It acts as a container for values.
Example:
```
x = 10
name = "Alice"
```

2. Rules for Variable Names

✅ Can contain letters, numbers, and underscores (_)

✅ Must start with a letter or underscore (not a number)

✅ Case-sensitive (Name and name are different)

❌ Cannot use Python keywords (for, if, class, etc.) Example:

user_name = "John"
UserName = "Mike"  # different from user_name

3. Assigning Values

Single assignment:
```
age = 25
```
Multiple assignment:
```
x, y, z = 1, 2, 3
```
Same value to multiple variables:
```
a = b = c = 0
```

4. Variable Types (Dynamic Typing)

No need to declare type — Python decides at runtime.

x = 5        # int
x = "Hello"  # now str

5. Data Types Commonly Used

int – integers (e.g., 10, -5)
float – decimal numbers (e.g., 3.14)
str – text strings (e.g., "Python")
bool – True or False
list, tuple, set, dict — collections

6. Constants

Python doesn’t have true constants — by convention, use UPPERCASE names.

PI = 3.14159

7. Deleting Variables

x = 10
del x

8. Type Casting

Convert between data types:

x = int("10")       # string to int
y = float(5)        # int to float
z = str(3.14)       # float to string

9. Checking Variable Type

a = [1, 2, 3]
print(type(a))  # <class 'list'>

10. Global & Local Variables

x = "global"

def test():
    x = "local"
    print(x)  # local

test()
print(x)      # global

Tags: Python Python Core