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Python Anonymous Function

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In this article, you’ll learn about the anonymous function, also known as lambda functions. You’ll learn what they are, their syntax and how to use them (with examples).

What are lambda functions in Python?

In Python, an anonymous function is a function that is defined without a name.

While normal functions are defined using the def keyword in Python, anonymous functions are defined using the lambda keyword.

Hence, anonymous functions are also called lambda functions.

How to use lambda Functions in Python?

A lambda function in python has the following syntax.

Syntax of Lambda Function in python

lambda arguments: expression

Lambda functions can have any number of arguments but only one expression. The expression is evaluated and returned. Lambda functions can be used wherever function objects are required.

Example of Lambda Function in python

Here is an example of lambda function that doubles the input value.

# Program to show the use of lambda functions
double = lambda x: x * 2

print(double(5))

Output

In the above program, lambda x: x * 2 is the lambda function. Here x is the argument and x * 2 is the expression that gets evaluated and returned.

This function has no name. It returns a function object which is assigned to the identifier double. We can now call it as a normal function. The statement

double = lambda x: x * 2

is nearly the same as:

def double(x):
   return x * 2

Use of Lambda Function in python

We use lambda functions when we require a nameless function for a short period of time.

In Python, we generally use it as an argument to a higher-order function (a function that takes in other functions as arguments). Lambda functions are used along with built-in functions like filter(), map() etc.

Example use with filter()

The filter() function in Python takes in a function and a list as arguments.

The function is called with all the items in the list and a new list is returned which contains items for which the function evaluates to True.

Here is an example use of filter() function to filter out only even numbers from a list.

# Program to filter out only the even items from a list
my_list = [1, 5, 4, 6, 8, 11, 3, 12]

new_list = list(filter(lambda x: (x%2 == 0) , my_list))

print(new_list)

Output

[4, 6, 8, 12]

Example use with map()

The map() function in Python takes in a function and a list.

The function is called with all the items in the list and a new list is returned which contains items returned by that function for each item.

Here is an example use of map() function to double all the items in a list.

# Program to double each item in a list using map()

my_list = [1, 5, 4, 6, 8, 11, 3, 12]

new_list = list(map(lambda x: x * 2 , my_list))

print(new_list)

Output

[2, 10, 8, 12, 16, 22, 6, 24]

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Python Functions

Introduction

Python Flow Control

Python Functions

Python Datatypes

Python Files

Python Object & Class

Python Advanced Topics

Python Date & Time

In this article, you’ll learn about functions, what a function is, the syntax, components, and types of functions. Also, you’ll learn to create a function in Python.

What is a function in Python?

In Python, a function is a group of related statements that performs a specific task.

Functions help break our program into smaller and modular chunks. As our program grows larger and larger, functions make it more organized and manageable.

Furthermore, it avoids repetition and makes the code reusable.

Syntax of Function

def function_name(parameters):
	"""docstring"""
	statement(s)

Above shown is a function definition that consists of the following components.

Keyword def that marks the start of the function header.
A function name to uniquely identify the function. Function naming follows the same rules of writing identifiers in Python.
Parameters (arguments) through which we pass values to a function. They are optional.
A colon (:) to mark the end of the function header.
Optional documentation string (docstring) to describe what the function does.
One or more valid python statements that make up the function body. Statements must have the same indentation level (usually 4 spaces).
An optional return statement to return a value from the function.

Example of a function

def greet(name):
    """
    This function greets to
    the person passed in as
    a parameter
    """
    print("Hello, " + name + ". Good morning!")

How to call a function in python?

Once we have defined a function, we can call it from another function, program or even the Python prompt. To call a function we simply type the function name with appropriate parameters.

>>> greet('Paul')
Hello, Paul. Good morning!

Note: Try running the above code in the Python program with the function definition to see the output.

def greet(name):
    """
    This function greets to
    the person passed in as
    a parameter
    """
    print("Hello, " + name + ". Good morning!")

greet('Paul')

Docstrings

The first string after the function header is called the docstring and is short for documentation string. It is briefly used to explain what a function does.

Although optional, documentation is a good programming practice. Unless you can remember what you had for dinner last week, always document your code.

In the above example, we have a docstring immediately below the function header. We generally use triple quotes so that docstring can extend up to multiple lines. This string is available to us as the __doc__ attribute of the function.

For example:

Try running the following into the Python shell to see the output.

>>> print(greet.__doc__)

    This function greets to
    the person passed in as
    a parameter

The return statement

The return statement is used to exit a function and go back to the place from where it was called.

Syntax of return

return [expression_list]

This statement can contain an expression that gets evaluated and the value is returned. If there is no expression in the statement or the return statement itself is not present inside a function, then the function will return the None object.

For example:

>>> print(greet("May"))
Hello, May. Good morning!
None

Here, None is the returned value since greet() directly prints the name and no return statement is used.

Example of return

def absolute_value(num):
    """This function returns the absolute
    value of the entered number"""

    if num >= 0:
        return num
    else:
        return -num


print(absolute_value(2))

print(absolute_value(-4))

Output

2
4

How Function works in Python?

Scope and Lifetime of variables

Scope of a variable is the portion of a program where the variable is recognized. Parameters and variables defined inside a function are not visible from outside the function. Hence, they have a local scope.

The lifetime of a variable is the period throughout which the variable exits in the memory. The lifetime of variables inside a function is as long as the function executes.

They are destroyed once we return from the function. Hence, a function does not remember the value of a variable from its previous calls.

Here is an example to illustrate the scope of a variable inside a function.

def my_func():
	x = 10
	print("Value inside function:",x)

x = 20
my_func()
print("Value outside function:",x)

Output

Value inside function: 10
Value outside function: 20

Here, we can see that the value of x is 20 initially. Even though the function my_func() changed the value of x to 10, it did not affect the value outside the function.

This is because the variable x inside the function is different (local to the function) from the one outside. Although they have the same names, they are two different variables with different scopes.

On the other hand, variables outside of the function are visible from inside. They have a global scope.

We can read these values from inside the function but cannot change (write) them. In order to modify the value of variables outside the function, they must be declared as global variables using the keyword global.

Types of Functions

Basically, we can divide functions into the following two types:

Built-in functions – Functions that are built into Python.
User-defined functions – Functions defined by the users themselves.

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C sharp, programming languages

C# Functions

Function is a block of code that has a signature. Function is used to execute statements specified in the code block. A function consists of the following components:

Function name: It is a unique name that is used to make Function call.

Return type: It is used to specify the data type of function return value.

Body: It is a block that contains executable statements.

Access specifier: It is used to specify function accessibility in the application.

Parameters: It is a list of arguments that we can pass to the function during call.

C# Function Syntax

FunctionName()
{
// function body
// return statement
}

Access-specifier, parameters and return statement are optional.

Let’s see an example in which we have created a function that returns a string value and takes a string parameter.

C# Function: using no parameter and return type

A function that does not return any value specifies void type as a return type. In the following example, a function is created without return type.

using System;
namespace FunctionExample
{
class Program
{
// User defined function without return type
public void Show() // No Parameter
{
Console.WriteLine(“Function Call without parameter”);
// No return statement
}

// Execution entry point of the program
static void Main(string[] args)
{
Program program = new Program(); // Creating Object
program.Show(); // Calling Function
}
}
}

output:

Function Call without parameter

C# Function: using parameter but no return type

using System;
namespace FunctionExample
{
class Program
{
// User defined function without return type
public void Show(string message)
{
Console.WriteLine(“Hello ” + message);
// No return statement
}

// Execution entry point of the program
static void Main(string[] args)
{
Program program = new Program(); // Creating Object
program.Show(“Students”); // Calling Function
}
}
}

Output:

Hello Students

C# Function: using parameter and return type

using System;
namespace FunctionExample
{
class Program
{
// User defined function
public string Show(string message)
{
Console.WriteLine(“Inside Show Function”);
return message;
}

// Execution entry point of the program
static void Main(string[] args)
{
Program program = new Program();
string message = program.Show(“Students”);
Console.WriteLine(“Hello “+message);
}
}
}

Output:

Inside Show Function
Hello Students

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