Python Closure

In this article, we will learn about python closures in detail with the help of examples and also learn prerequisites like nested functions which help us understand python closures in a clear manner.

We will see some observations about python closures and discuss non-local variables.

Finally, where should we use the python closures? And some conditions when we can use python closures.

Next, we will see Python Closures but before that let’s discuss the nested functions in python.

Nested Function in Python :

Nested functions can access and modify variables that are defined in their parent functions, which is the main distinction between them and other types of functions.
Some Points about nested functions are :

  1. Variables that are not explicitly passed as input arguments can be used by nested functions.
  2. You may build a handle to a nested function in a parent function that holds the information required to execute the nested function.

It is a function inside a function for example:

def external():
    say = 'Hello'
    def internal():
    return internal

The closure is made up of the "internal" function and the "say" variable.

Python Closure:

A nested function called a "python closure" enables us to access variables from an outer function even after it has been closed.

A closure is a type of function object that retains values from scopes around it even when they are not in memory.

In Python, closure refers to an inner function object that operates like an object, remembers the local variables it was created with, and retains access to them even after the outer function has done executing.

It can also be defined as a technique for binding data to a function without actually passing it as a parameter.

Let’s understand this concept using an example given below:

Code implementation:

def external(text):  
    #inner function  
    def internal():  
external('Learn at prepbytes')


Learn at prepbytes

We will discuss a few things that you may describe as anomalies in this piece of code in this article. As an illustration, consider a nested function, a variable that was declared in an external function but was used by an internal function, and an external function that returned a function instead of a variable.

Now let’s understand what we did in this program-

  1. A function “external” that takes the parameter text has been developed, and inside of it, another function that prints the value of text has also been made.
  2. As we can clearly see, the program above calls ‘internal’ function and we then send a string value to external function.
  3. When this program is executed, the expected result is shown.

Based on the above learning we have the following observations-

  1. We will invoke functions that can be outside the scope in python, with the assistance of closure.
  2. Closure, as defined here, is a function object that keeps track of the values in the contained scope.
  3. Each variable in a function is mapped to its value or a reference to its name in a record called a closure in Python.
  4. It helps us to access the variables using closure copies.

These are some of the observations we got so far from our learning.

Non-local Keyword:

To specify that a variable is not local, use the phrase nonlocal, Below are some of the points related to it-

  • The nonlocal keyword is used when working with variables inside nested functions when the variable should not be a member of the inner function.
  • With the nonlocal keyword, we can change an immutable type variable in the outside function scope.
  • Each variable has a defined scope. The scope is essentially the section of the program’s code where the variable can be identified and reached if necessary.

To create global variables, use the keyword ‘global’.

Uses of Python Closures:

Below are the features and uses of python closures where it should be used-

  1. Closures offer some sort of data hiding because they are used as callback functions. As a result, we use fewer global variables.
  2. Closures can be implemented as an alternative for global scope.
  3. An essential application of closures is data hiding.
  4. Closures appear to be an effective method when we only have a few functions in our code. However, if we require a lot of functions, we should use classes (OOP).
  5. Closures can be used to prevent using classes in unnecessary situations.
  6. Closures are widely used by Python decorators as well.

When we can use a Closure:

There are certain conditions when we can use python closures which are as follow-

  1. There must be nested functions in program.
  2. The enclosed function’s value must be referred by the function.
  3. The nested function must be returned by the enclosing function.

Here is the conclusion what we have learnt in this article so far-

  • In general, a Python closure is a nested function with some data associated with it.
  • Learnt from the above example how to call python closures.
  • It has availability to a free variable inside the outer scope.
  • Functions outside of their scope can be called with the aid of closures.
  • Learn about Free variable -a variable which is not bound in the local space. The nonlocal keyword is necessary for closures to function with immutable variables such as strings and integers.

So, in this article, we learnt in detail what python closures are and when we may use them to increase the effectiveness of our programs.

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