Python Variables

What is a Variable?

Variables are the reserved memory locations to store values(data). This means that when you create a variable you reserve some space in memory.

Location of Variable

id is used to find the address or location of the variables.

# id is used to find the address of the variables 
age = 20
print(id(age))

name ="Python"
print(id(name))

company = "" 
print(id(company))

Output:
140736363164000
1534947487848
1534917180528

Rules for Python Variables

An variable is a sequence of letters such as uppercase(A to Z),lowercase(a to z),digits(0 to 9) and an underscore (_) ie “Alphanumeric “ characters.

It does not allow punctuation characters such as @, $, and % within variable.

It is a case sensitive ( Eg: Students and student are different variable)

Reserved words cannot be used as variable.

It cannot start with a digit. (Python thinks it is a number)

Eg: 1student is invalid 
     student1 is valid

Creating and Assigning Values to Variables

A variable is created the moment you first assign a value to it. The equal sign (=) is used to assign values to variables.

# Declaring the variables 
rollnumber  = 12345 # rollnumber  is integer
name = "Santosh" # name is string
marks = 80.5  # marks is float
print(rollnumber,name,marks)

Output:
12345 Santosh 80.5

Conclusion: Python variables do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable. Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Note: An interpreter is a program that reads and executes code

Multiple Assignment

# 1. Multiple variables in single row
a,b,c,d = 10,20,30,40
print(a,b,c,d)

Output:
10 20 30 40

# 2. Multiple variables of different data types
name,rollnumber,marks="Santosh",12345,85.75
print(name,rollnumber,marks)

Output:
Santosh 12345 85.75

# 3. Single value to several variables
graph1 = graph2 = graph3 = "DataScience"
print(graph1,graph2,graph3)

Output:
DataScience DataScience DataScience

Memory Allocation

If the value is same, the memory location will be also same.

# id is used to find the address of the varaible
print(id(graph1))
print(id(graph2))

Output:
1534987626544
1534987626544

# Updating the value of varible (graph2) and checking the memory location
graph2= "Python"
print(id(graph2))

Output:
1534947487848

Conclusion: The performance of our coding depends on 2 things.
1. Code logic
2. Memory allocation(how we handle variables)