In this tutorial, we will discuss the variable use in python and how they are categorized in Global, local and Non-local.
Python Global Variables
All those variables in python which are declared outside the function in a global scope are known asa global variable. In simple words any statement of the programme that can access a variable that variable is a global variable.
Let’s understand it with an example:
global_variable = 20 #Global Variable
def func(): #defining a function
print("the value of global_variable is " + str(global_variable))
func() #function calling
#Output
the value of global_variable is 20
Behind the code:
In the above example, we have first we declared a variable global_variable and assigned value 20 to it and then we defined a function func() which is printing the output value of global_variable.
So what is happening here, when we are calling the function func() the function func() gets started to execute and it reaches to the print statement and at the print() statement first the function looks for the globle_variable inside itself but when it could not find it inside the function func() then it starts looking for it outside the function and then print the value.
Local Variable
All those variables that we defined inside the function are known as a local variable and you cannot access them outside the function.
Let’s understand it with an example:
g = "global variable" def local(): l = "local variable" print(g) # printing global variable print(l) # print local variable local()
#Output
global variable local variable
Behind the code:
In the above example, g is a global variable and l is a local variable. You can see that we can access the g inside the function local and we can access it outside the function but if you try to access the variable l outside the function it will throw an error.
Let’s call a local variable outside the function:
def local(): l = "local variable" # l is a local variable local() print(l) # Accessing local variable outside the function
#Output
NameError: name 'l' is not defined
Behind the code:
As we said earlier that we cannot access the local variable outside the function. if we try to access it, we will get an error such as variable not defined.
Global keyword in python
global is a keyword in python which is used to access the actual global variable from outside the function. Until now we know that we can access the global variable from outside the function but if you alter the global variable or assign a new object or value to it inside the function it will become a local variable and this has no impact on the actual global variable which is present outside the function.
if you want o to grab a variable which is outside the function and want to make changes on there we need a keyword global which can grab the global variable and we can alter them inside the function.
let’s understand it with an example.
global_variable_1 = 20
global_variable_2 = 30
def local():
global global_variable_1 #here we have access the actual global_variable_1 which is present outside the function
global_variable_2 = 70 #it is a local variable having the same name as the global variable
global_variable_1 = 80 #here we have changed the value of globle_variable_1 which will reflect outside the function too
local()
print("the value of global_variable_1 has become", global_variable_1)
print("the value of global_variable_2 did not change" , global_variable_2)
#Output
the value of global_variable_1 has become 80 the value of global_variable_2 did not change 30
Behind the code:
In the above example we use the global keyword to access only one global variable which is global_variable_1 and all those changes we make on global_variable_1 remain same though we change the value of variable global_variable_2 but it changes for the local() function itself it did not reflect it outside the function like global_variable_1 because we did not grab it from outside the function it is a local variable having the same name as global variable but it has nothing to do with the actual global_variable_2.
Let’s take another example but here we do not use the global keyword:
var = 30 # global variable
def local():
var = 30 #local variable
var = var +40
print("var inside the local function",var)
local()
print("var outside the function", var)
#Output:
var inside the local function 70 var outside the function 30
Same example with global keyword
var = 30 # global variable
def local():
global var #global variable
var =var+ 40
print("var inside the local function ",var)
local()
print("var outside the function", var)
#Output
var inside the function local 70 var outside the function 70
Nonlocal Variable
nonlocal is a keyword which acts as a global keyword for the nested function (function inside another function). We use the nonlocal keyword when a variable is in local scope but act as a global scope for another function.
let’s understand it with an example:
def local():
x = 70
def in_local():
nonlocal x #here we grab the actual x variable which is a local variable
x = 70000
print("value of x inside the in_local function is", x)
in_local() #calling function in_local
print("the value of x inside the function local has become", x)
local()
#Output
value of x inside the in_local function is 70000 the value of x inside the function local has become 70000
Behind the function:
Though variable x of local() function is a local variable but it act as global variable for the function in_local(). When we use the keyword nonlocal to grab the variable x and use it inside the nested function in_local() and every change we make inside the in_local function on variable x reflect back on the original value of x.
perfect one … i loved it ..