Python Programming: Data Types, Variables, Scope & Practical Guide

4. Data Types & Examples

Python has several built-in data types used to define various operations and storage behaviors.

Data Type	Description	Example Code	Output
int	Integer numbers	`a = 25` `print(type(a))`	`<class 'int'>` `25`
float	Decimal numbers	`b = 3.14` `print(type(b))`	`<class 'float'>` `3.14`
str	Text / String	`s = "Hello"` `print(type(s))`	`<class 'str'>` `Hello`
bool	True or False	`flag = False` `print(type(flag))`	`<class 'bool'>` `False`
list	Ordered collection (mutable)	`lst = [1, 2, 3]` `print(type(lst))`	`<class 'list'>` `[1, 2, 3]`
tuple	Ordered collection (immutable)	`tup = (1, 2, 3)` `print(type(tup))`	`<class 'tuple'>` `(1, 2, 3)`
dict	Key-Value pairs	`d = {"a": 1, "b": 2}` `print(type(d))`	`<class 'dict'>` `{'a': 1, 'b': 2}`

5. Assigning Multiple Variables

Python allows flexible assignment patterns for initializing and manipulating values across multiple variables simultaneously.

Assign same value to multiple variables:

a = b = c = 100
print(a, b, c)  # Output: 100 100 100

Assign different values to multiple variables:

a, b, c = 10, 20, 30
print(a, b, c)  # Output: 10 20 30

Swap two variables:

a, b = 5, 10
a, b = b, a
print(a, b)  # Output: 10 5

6. Variable Scope

Scope determines the visibility and lifecycle of variables within your code blocks.

x = "Global"  # Global variable

def func():
    y = "Local"  # Local variable
    print("Inside function, y =", y)

func()
# print(y)  # Error! y is not accessible outside the function
print("Outside function, x =", x)

Output:

Inside function, y = Local
Outside function, x = Global

7. Type Conversion

You can explicitly convert data from one type to another using built-in casting functions.

x = "100"
print(int(x) + 50)  # Output: 150

y = 3.99
print(int(y))       # Output: 3

z = 10
print(str(z) + " is number")  # Output: 10 is number

flag = "True"
print(bool(flag))   # Output: True

Common Type Conversion Functions

int() – converts to integer
float() – converts to float
str() – converts to string
bool() – converts to boolean
list() – converts to list
tuple() – converts to tuple
dict() – converts to dictionary

8. Constants (By Convention)

PI = 3.14159     # Constant (by convention - use UPPERCASE)
MAX_USERS = 100

Note: Python does not enforce true immutable constants syntactically, but developers use UPPERCASE naming conventions to indicate values that should remain constant.

9. Delete Variables

You can remove variables from memory using the del keyword.

a = 10
print(a)  # Output: 10

del a     # Delete variable reference
# print(a)  # Error: name 'a' is not defined

10. Check if Variable Exists

You can verify whether a variable has been defined in the global scope using globals().

x = 50

if 'x' in globals():
    print("x exists")
else:
    print("x does not exist")

Output:

x exists

11. Practical Example

Bringing concepts together with basic variable declarations and formatted strings (f-strings):

name = "John"
age = 25
is_emp = True
salary = 55000.75

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Employed: {is_emp}")
print(f"Salary: {salary}")

Output:

Name: John
Age: 25
Employed: True
Salary: 55000.75