Python nonlocal keyword is used to reference a variable in the nearest scope.
Python nonlocal Keyword Example
In this example, we demonstrate the working of the nonlocal keyword.
Python3
def foo(): name = "geek" # Our local variable def bar(): nonlocal name # Reference name in the upper scope name = 'GeeksForGeeks' # Overwrite this variable print(name) # Calling inner function bar() # Printing local variable print(name)foo() |
GeeksForGeeks GeeksForGeeks
What is nonlocal keyword in Python
The nonlocal keyword won’t work on local or global variables and therefore must be used to reference variables in another scope except the global and local one. The nonlocal keyword is used in nested functions to reference a variable in the parent function.
Advantages of nonlocal:
- It helps in accessing the variable in the upper scope.
- Since the referenced variable is reused, the memory address of the variable is also reused and therefore it saves memory.
Disadvantages of nonlocal:
- The nonlocal keyword can’t be used to reference global or local variables.
- The nonlocal keyword can only be used inside nested structures.
Example 1: In this example, we see what happens when we make a nonlocal variable to refer to the global variable.
Python3
# Declaring a global variableglobal_name = 'neveropen'def foo(): # Defining inner function def bar(): # Declaring nonlocal variable nonlocal global_name # Try to reference global variable global_name = 'GeeksForGeeks'# Try to overwrite it print(global_name) # Calling inner function bar() foo() |
Output:
SyntaxError: no binding for nonlocal 'name' found
Example 2: In this example, we will see which variable nonlocal refers to when we have multiple nested functions with variables of the same name.
Python3
def foo(): # Local variable of foo() name = "geek" # First inner function def bar(): name = "Geek" # Second inner function def ack(): nonlocal name # Reference to the next upper variable with this name print(name) # Print the value of the referenced variable name = 'GEEK' # Overwrite the referenced variable print(name) ack() # Calling second inner function bar() # Calling first inner function print(name) # Printing local variable of bar()foo() |
Output
Geek GEEK geek
Example 3: In this example, we will build a reusable counter (Just for demonstration purpose
Python3
# Our counter functiondef counter(): c = 0 # Local counter variable # This function manipulate the # local c variable, when called def count(): nonlocal c c += 1 return c # Return the count() function to manipulate # the local c variable on every call return count# Assign the result of counter() to# a variable which we use to count upmy_counter = counter()for i in range(3): print(my_counter())print('End of my_counter') # Create a new counternew_counter = counter()for i in range(3): print(new_counter())print('End of new_counter') |
Output
1 2 3 End of my_counter 1 2 3 End of new_counter
Note: Notice how the local c variable keeps alive on every call of our counter variables.
