Closure in Python

In this article, we will learn what a closure is, how to create a closure function, its benefits, and its applications. Let’s start with nested functions.

Nested Functions in Python

In Python, we can define a function inside another function. The function within another function is called a Nested Function. The function in which a Nested function is defined is called an Enclosed function.

Example of Nested Functions in Python

def func1():

   var = "PythonGeeks"

   def func2():
       print(var)

   func2()

func1()

Output

In the above code example, the function func2() is the Nested function and the function func1() is called the Enclosed function.

Nonlocal variables in Python

Variables that are defined in the enclosing function, but not in the nested function are known as Nonlocal variables. A nested function can access any nonlocal variable of its enclosing function.

Example of nonlocal variables in Python

def func1():

   var = "PythonGeeks"

   def func2():
       print(var)

   func2()

func1()

Output

In the above code example, the variable var is the nonlocal variable. The nested function accessed it even though it is outside of the nested function scope.

By default, a nested function can’t modify nonlocal variables.

Example of nonlocal variable in Python

def func1():

   var = "Enclosed Function"

   def func2():
       var = "Nested Function"
       print(var)
   func2()
   print(var)

func1()

Output

We must use the keyword nonlocal and declare the variable in the nested function to modify a nonlocal variable from a nested function.

Example of nonlocal variable in Python

def func1():

   var = "Enclosed Function"

   def func2():
       nonlocal var
       var = "Nested Function"
       print(var)
   func2()
   print(var)

func1()

Output

In the above code example, the nested function func2() modified the variable var which is in the scope of enclosed function func1().

Closure in Python

To understand the concept of closure, let us first define a closure function. To define a closure function, we need to first define a nested function that reads one or more nonlocal variables and finally return the nested function.

Example of a closure function in Python

def forest():

   animals = 200

   def population():

       return animals

   return population

amazon = forest()
print(amazon())

Output

In the above code example, the function population() is the closure function.

Let us delete the enclosed function and see what happens.

Example of a closure function in Python

def forest():

   animals = 200

   def population():

       return animals

   return population

amazon = forest()

del forest

print(amazon())

Output

In the above code example, Even after we deleted the enclosed function, the nested function still accessed the values of nonlocal variables and ran without raising any errors.

This happens because Python creates an environment for the nested function by connecting the values of nonlocal variables to the nested function.

This method of remembering the values of nonlocal variables even if the variables are no longer in scope or the function is no longer in the current namespace is called Closure.

Requirements of Python closure function

We must meet the following requirements to create a closure function.

1. Define a nested function
2. Return the Nested function
3. The Nested function should access a nonlocal variable.

Advantages of closure in Python

The following are some of the well-known benefits of closure in Python:

1. Avoid the usage of global variables
2. Makes code look elegant
3. Data hiding
4. Preferred more than classes when working with a few number of functions.
5. Rather than implementing classes, implementing closure is more efficient.

Uses of Closure in Python

One of the most common applications of closure in Python is decorators. The core principle of the decorator is based on closure.

Example of closure in Python

def math(func):

   def div(numerator, denominator):
       if denominator == 0:
           return "Zero Division Error"
       return func(numerator, denominator)
   return div

@math
def division(a, b):
   return a/b

print(division(4, 2))
print(division(4, 0))

Output

Python Interview Questions on Closure in Python

Q1. Define a nested function student() within the function school(). Define a nonlocal variable day=”Sunday” and use the nested function to print that variable.

Ans 1. Complete code is as follows:

def school():

   day = "Sunday"

   def student():
       print(day)

   student()

school()

Output

Q2. Define a function create_powers(X) which returns a function power(Y) which returns YX.

Ans 2. Complete code is as follows:

def create_powers(num):

   def power(n):

       return pow(n, num)

   return power

cube = create_powers(3)
print(cube(2))
square = create_powers(2)
print(square(2))

Output

Q3. What is the output of the below code?

def func1():
   var1 = "Python"

   def func2():
       var2 = "Geeks"
       return var1+var2

   return func2

func3 = func1()
print(func3())

Ans 3. The output of the given code is:

Q4. Does the below code raise any error. If not, then what is the output of the below code?

def city():
   men = 50000
   women = 48000
   children = 25000

   def get_total():
       return men+women+children

   return get_total

population = city()

del city

print(population())

Ans 4. The given code doesn’t raise any errors and its output is:

Q5. Show an application of closure in Python.

Ans 5. The most common application of closure is decorators in Python.

Complete code is as follows:

def city():
   men = 50000
   women = 48000
   children = 25000

   def get_total():
       return men+women+children

   return get_total

population = city()

del city

print(population())

Output

Conclusion

In this article, we learned about closure in Python. See how to create a closure function and its benefits. Then learn about the most common application of closure in Python. Additionally, please feel free to post any queries in the comments section.