Python Variables

Hello everyone⚡, In this article, we will learn about Python Variables.

Introduction

Variables are important to understand to work with any programming language. It is used to store information.

Variables or Identifiers

• The memory location name is called variable and variable is also known as an identifier. it is used to store and process the information.
• Variable names can be a group of both the letters and digits, but they have to begin with a letter or an underscore.

syntax : name = value

example : a = 10, b = 4.5

In Python, The variable is described in two categories

1. Local variable
2. Global variable.

Local variable:

• local variable means defining a variable inside the function.
• We can access the local variables directly, local variables available only inside the same function to access. Let's understand the following example.

  def fun():
    a=12    #local
    print("A = ",a)
  fun()      #calling
  

  Output:
  A = 12
  

• Arguments of a function work like local variables, hence we can access arguments only from the same functions.

Let's understand the following example.

def fun(x,y):
    print("X value =",x)
    print("Y value =",y)
fun(12,20)

Output:
X value = 12
Y value = 20

Global Variable:

• Global variable means defining a variable outside of all the functions.
• We can access global variables directly.
• Global variable available throughout the source file .

Let's understand the following example.

a=10 #global
def fun1():
    print("A =",a)
def fun2():
    print("B =",a)
fun1()  #calling function
fun2()
print("C =",a)

Output:
A = 10
B = 10
C = 10

Special case:

• Local and global variables can have the same name.
• Where we access the variables directly inside the function. It gives the first priority to local variable.

Let's understand the following example.

a=10 #global
def fun1():
    a=20
    print("A =",a)
def fun2():
    print("B =",a)
fun1()  #calling function
fun2()
print("outside =",a)

Output:
A = 20
B = 10
outside = 10

Can not access variables/identifiers before declaration

• Python is interpreted programming language, Hence the source code executes line by line.
• Because of interpretation we can not access the members before definitions.

Let's understand the following Program.

test()     #Error: name 'test' is not defined
def fun():
    print("test")
test()

• We can access variables after memory allocation.

Let's understand the following Program.

def fun():
    print("test = ", a)
fun()   #Error: name 'a' is not defined
a=10    #global
fun()   # output:  test =  10

Note

We can access global variable inside the function but we can not modify

Let's understand the following Program.

a=10
def test():
    print("a =",a)
    a=a+10      #Error: local variable 'a' referenced before assignment
    print("a =",a)
test()

How to use Global keyword

• It is the keyword.
• It is used to access global variables inside the function. Let's understand the following Program.

a=10
def fun():
    global a
    print("a=",a)
    a=a+10
    print("a=",a)
    a=a+25
fun()
print("a=",a)

Output:
a= 10
a= 20
a= 45

Note

Inside the function, we use either local variable or global variable with the same name.

• We need to specify the global statement inside the function before the use of variable.
• Once we use local variable inside the function, we can not access global variable. Let's understand the following Program.

a=10        #global
def fun():
    a=20        #local
    print("a=",a)
    global a    #Error: name 'a' is used prior to global declaration
    print("a=",a)
fun()

Program - If variables are different, we can access them as follows.

a=10        #global
def fun():
    b=20        #local
    print("b=",b)
    global a    
    print("a=",a)
fun()

Output:
b= 20
a= 10

• We can create global variables inside the function. program -

def fun():
    global a
    a=10
    print("a=",a)
    a=a+20    
fun()
print("a=",a)

Output:
a= 10
a= 30

To delete a variable, Use the keyword "del"

A pre-defined keyword "del", which is used to release the memory allocated to a variable.

Let's understand the following Program.

def Create():
    global a
    a=10
    print("Initial value = ",a)
def modify():
    global a
    a=a+10
    print("modified value=",a)
def delete():
    global a
    del a 
    print("a value=",a)     
Create()
modify()
delete()

Output
Initial value =  10
modified value= 20

Traceback (most recent call last):
File "<string>", line 15, in <module>
File "<string>", line 12, in delete
NameError: name 'a' is not defined

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