Closure

Definition

Closure is a function that has access to variables from an outer function, even after the outer function has finished executing. It allows the inner function to 'remember' and continue to use the variables from the outer function's scope, even after the outer function has returned.

5 Must Know Facts For Your Next Test

1. Closures are created when a function is defined within another function, and the inner function references variables from the outer function's scope.
2. Closures 'remember' the values of the variables from the outer function, even after the outer function has finished executing and returned.
3. Closures can be used to create private variables and methods, as well as to create functions with persistent state.
4. Closures are a fundamental concept in functional programming, and they are widely used in JavaScript to achieve data encapsulation and higher-order functions.
5. Closures are often used to create callback functions, event handlers, and other asynchronous constructs in JavaScript.

Review Questions

• Explain how closures relate to variable scope in Python.
  • Closures in Python are closely tied to variable scope. When a function is defined within another function, the inner function has access to variables from the outer function's scope, even after the outer function has finished executing. This is because the inner function 'closes over' the variables it needs from the outer function, creating a closure. Closures allow the inner function to 'remember' and continue to use these variables, even when the outer function has returned.
• Describe how nested functions and lexical scoping contribute to the creation of closures.
  • Nested functions, where a function is defined within another function, are a key component of closures. The inner function has access to variables in its own scope, as well as variables from the scope of the outer function(s). This is due to the concept of lexical scoping, where the visibility of a variable is determined by its physical location in the source code. The location of the variable declaration defines its scope. When an inner function references variables from the outer function's scope, it creates a closure that 'remembers' those variables, even after the outer function has finished executing.
• Evaluate the use of closures in Python for creating private variables and methods, as well as for implementing higher-order functions.
  • Closures in Python are widely used to achieve data encapsulation and create higher-order functions. By defining a function within another function and having the inner function access variables from the outer function's scope, you can create private variables and methods that are hidden from the global scope. This is a fundamental concept in functional programming and is used extensively in Python to implement callback functions, event handlers, and other asynchronous constructs. Additionally, closures allow for the creation of functions that can 'remember' and operate on state from previous function calls, enabling the implementation of higher-order functions and more complex programming patterns.

Related terms

Scope:

Scope refers to the visibility and accessibility of variables and functions in different parts of a program. It determines where variables and functions can be accessed or modified.

Lexical Scoping: Lexical scoping is a type of scope where the visibility of a variable is determined by its physical location in the source code. The location of the variable declaration defines its scope.

Nested Functions: Nested functions are functions defined within other functions. They have access to variables in their own scope, as well as variables in the scope of the outer function(s).