- Python Basics
- Python - Home
- Python - Overview
- Python - History
- Python - Features
- Python vs C++
- Python - Hello World Program
- Python - Application Areas
- Python - Interpreter
- Python - Environment Setup
- Python - Virtual Environment
- Python - Basic Syntax
- Python - Variables
- Python - Data Types
- Python - Type Casting
- Python - Unicode System
- Python - Literals
- Python - Operators
- Python - Arithmetic Operators
- Python - Comparison Operators
- Python - Assignment Operators
- Python - Logical Operators
- Python - Bitwise Operators
- Python - Membership Operators
- Python - Identity Operators
- Python - Operator Precedence
- Python - Comments
- Python - User Input
- Python - Numbers
- Python - Booleans
- Python Control Statements
- Python - Control Flow
- Python - Decision Making
- Python - If Statement
- Python - If else
- Python - Nested If
- Python - Match-Case Statement
- Python - Loops
- Python - for Loops
- Python - for-else Loops
- Python - While Loops
- Python - break Statement
- Python - continue Statement
- Python - pass Statement
- Python - Nested Loops
- Python Functions & Modules
- Python - Functions
- Python - Default Arguments
- Python - Keyword Arguments
- Python - Keyword-Only Arguments
- Python - Positional Arguments
- Python - Positional-Only Arguments
- Python - Arbitrary Arguments
- Python - Variables Scope
- Python - Function Annotations
- Python - Modules
- Python - Built in Functions
- Python Strings
- Python - Strings
- Python - Slicing Strings
- Python - Modify Strings
- Python - String Concatenation
- Python - String Formatting
- Python - Escape Characters
- Python - String Methods
- Python - String Exercises
- Python Lists
- Python - Lists
- Python - Access List Items
- Python - Change List Items
- Python - Add List Items
- Python - Remove List Items
- Python - Loop Lists
- Python - List Comprehension
- Python - Sort Lists
- Python - Copy Lists
- Python - Join Lists
- Python - List Methods
- Python - List Exercises
- Python Tuples
- Python - Tuples
- Python - Access Tuple Items
- Python - Update Tuples
- Python - Unpack Tuples
- Python - Loop Tuples
- Python - Join Tuples
- Python - Tuple Methods
- Python - Tuple Exercises
- Python Sets
- Python - Sets
- Python - Access Set Items
- Python - Add Set Items
- Python - Remove Set Items
- Python - Loop Sets
- Python - Join Sets
- Python - Copy Sets
- Python - Set Operators
- Python - Set Methods
- Python - Set Exercises
- Python Dictionaries
- Python - Dictionaries
- Python - Access Dictionary Items
- Python - Change Dictionary Items
- Python - Add Dictionary Items
- Python - Remove Dictionary Items
- Python - Dictionary View Objects
- Python - Loop Dictionaries
- Python - Copy Dictionaries
- Python - Nested Dictionaries
- Python - Dictionary Methods
- Python - Dictionary Exercises
- Python Arrays
- Python - Arrays
- Python - Access Array Items
- Python - Add Array Items
- Python - Remove Array Items
- Python - Loop Arrays
- Python - Copy Arrays
- Python - Reverse Arrays
- Python - Sort Arrays
- Python - Join Arrays
- Python - Array Methods
- Python - Array Exercises
- Python File Handling
- Python - File Handling
- Python - Write to File
- Python - Read Files
- Python - Renaming and Deleting Files
- Python - Directories
- Python - File Methods
- Python - OS File/Directory Methods
- Python - OS Path Methods
- Object Oriented Programming
- Python - OOPs Concepts
- Python - Classes & Objects
- Python - Class Attributes
- Python - Class Methods
- Python - Static Methods
- Python - Constructors
- Python - Access Modifiers
- Python - Inheritance
- Python - Polymorphism
- Python - Method Overriding
- Python - Method Overloading
- Python - Dynamic Binding
- Python - Dynamic Typing
- Python - Abstraction
- Python - Encapsulation
- Python - Interfaces
- Python - Packages
- Python - Inner Classes
- Python - Anonymous Class and Objects
- Python - Singleton Class
- Python - Wrapper Classes
- Python - Enums
- Python - Reflection
- Python Errors & Exceptions
- Python - Syntax Errors
- Python - Exceptions
- Python - try-except Block
- Python - try-finally Block
- Python - Raising Exceptions
- Python - Exception Chaining
- Python - Nested try Block
- Python - User-defined Exception
- Python - Logging
- Python - Assertions
- Python - Built-in Exceptions
- Python Multithreading
- Python - Multithreading
- Python - Thread Life Cycle
- Python - Creating a Thread
- Python - Starting a Thread
- Python - Joining Threads
- Python - Naming Thread
- Python - Thread Scheduling
- Python - Thread Pools
- Python - Main Thread
- Python - Thread Priority
- Python - Daemon Threads
- Python - Synchronizing Threads
- Python Synchronization
- Python - Inter-thread Communication
- Python - Thread Deadlock
- Python - Interrupting a Thread
- Python Networking
- Python - Networking
- Python - Socket Programming
- Python - URL Processing
- Python - Generics
- Python Libraries
- NumPy Tutorial
- Pandas Tutorial
- SciPy Tutorial
- Matplotlib Tutorial
- Django Tutorial
- OpenCV Tutorial
- Python Miscellenous
- Python - Date & Time
- Python - Maths
- Python - Iterators
- Python - Generators
- Python - Closures
- Python - Decorators
- Python - Recursion
- Python - Reg Expressions
- Python - PIP
- Python - Database Access
- Python - Weak References
- Python - Serialization
- Python - Templating
- Python - Output Formatting
- Python - Performance Measurement
- Python - Data Compression
- Python - CGI Programming
- Python - XML Processing
- Python - GUI Programming
- Python - Command-Line Arguments
- Python - Docstrings
- Python - JSON
- Python - Sending Email
- Python - Further Extensions
- Python - Tools/Utilities
- Python - GUIs
- Python Useful Resources
- Python Compiler
- NumPy Compiler
- Matplotlib Compiler
- SciPy Compiler
- Python - Questions & Answers
- Python - Online Quiz
- Python - Programming Examples
- Python - Quick Guide
- Python - Useful Resources
- Python - Discussion
Python - Closures
In this chapter, let us discuss the concept of closures in Python. In Python, functions are said to be first order objects. Just like the primary data types, functions can also be used assigned to variables, or passed as arguments.
Nested Functions
You can also have a nested declaration of functions, wherein a function is defined inside the body of another function.
Example
def functionA(): print ("Outer function") def functionB(): print ("Inner function") functionB() functionA()
It will produce the following output −
Outer function Inner function
In the above example, functionB is defined inside functionA. Inner function is then called from inside the outer function's scope.
If the outer function receives any argument, it can be passed to the inner function.
def functionA(name): print ("Outer function") def functionB(): print ("Inner function") print ("Hi {}".format(name)) functionB() functionA("Python")
It will produce the following output −
Outer function Inner function Hi Python
What is a Closure?
A closure is a nested function which has access to a variable from an enclosing function that has finished its execution. Such a variable is not bound in the local scope. To use immutable variables (number or string), we have to use the nonlocal keyword.
The main advantage of Python closures is that we can help avoid the using global values and provide some form of data hiding. They are used in Python decorators.
Example
def functionA(name): name ="New name" def functionB(): print (name) return functionB myfunction = functionA("My name") myfunction()
It will produce the following output −
New name
In the above example, we have a functionA function, which creates and returns another function functionB. The nested functionB function is the closure.
The outer functionA function returns a functionB function and assigns it to the myfunction variable. Even if it has finished its execution. However, the printer closure still has access to the name variable.
nonlocal Keyword
In Python, nonlocal keyword allows a variable outside the local scope to be accessed. This is used in a closure to modify an immutable variable present in the scope of outer variable.
Example
def functionA(): counter =0 def functionB(): nonlocal counter counter+=1 return counter return functionB myfunction = functionA() retval = myfunction() print ("Counter:", retval) retval = myfunction() print ("Counter:", retval) retval = myfunction() print ("Counter:", retval)
It will produce the following output −
Counter: 1 Counter: 2 Counter: 3