Python Variables

Python Basics Python Introduction Python Installation Overview of Jupyter IDE Identifiers & Reserved Keywords Python Variables Python Numbers Python Operators Python Operators and Arithmetic Operators Comparison and Logical Operators Assignment and Bitwise Operators Identity and Membership Operators Python Flow Control if else if else statement While Loop Statement Python For Loop Break and Continue Statement Python Data Types Python Strings Python Strings Methods Python Lists Python Tuples Python Dictionary Python Functions Introduction to Python Functions Function Arguments Recursion Function Lambda/Anonymous Function Python - Modules Python Files Python - Files I/O Python - Exceptions Handling Python - Debugging

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)