global keyword allows us to modify the variable outside of the current scope. It is used to create a global variable and make changes to the variable in a local context.
Before we learn about the
global keyword, make sure you have got some basics of Python Variable Scope.
Access and Modify Python Global Keyword/Variable
First let’s try to access a global variable from the inside of a function,
c = 1 # global variable def add(): print(c) add() # Output: 1
Here, we can see that we have accessed a global variable from the inside of a function.
However, if we try to modify the global variable from inside a function as:
# global variable c = 1 def add(): # increment c by 2 c = c + 2 print(c) add()
OutputUnboundLocalError: local variable 'c' referenced before assignment
This is because we can only access the global variable but cannot modify it from inside the function.
The solution for this is to use the
Example: Changing Global Variable From Inside a Function using global
# global variable c = 1 def add(): # use of global keyword global c # increment c by 2 c = c + 2 print(c) add() # Output: 3
In the above example, we have defined c as the
global keyword inside
Then, we have incremented the variable c by 2, i.e
c = c + 2.
As we can see while calling
add(), the value of global variable c is modified from 1 to 3.
Global in Nested Functions
In Python, we can also use the
global keyword in a nested function. For example,
def outer_function(): num = 20 def inner_function(): global num num = 25 print("Before calling inner_function(): ", num) inner_function() print("After calling inner_function(): ", num) outer_function() print("Outside both function: ", num)
OutputBefore calling inner_function(): 20 After calling inner_function(): 20 Outside both function: 25
In the above example, we declared a global variable inside the nested function
outer_function(), num has no effect of the
Before and after calling
inner_function(), num takes the value of the local variable i.e
num = 20.
Outside of the
outer_function() function, num will take the value defined in the
inner_function() function i.e
x = 25.
This is because we have used the
global keyword in num to create a global variable inside the
inner_function() function (local scope).
So, if we make any changes inside the
inner_function() function, the changes appear outside the local scope, i.e.
Rules of Python global Keyword
The basic rules for
global keyword in Python are:
- When we create a variable inside a function, it is local by default.
- When we define a variable outside of a function, it is global by default. You don’t have to use the
- We use the
globalkeyword to read and write a global variable inside a function.
- Use of the
globalkeyword outside a function has no effect.