Python Anonymous (Lambda) Function

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Python Anonymous (Lambda) Function, means a function without a name.

As we have already discussed that, to define a function in Python we use the def keyword, but to define an anonymous (lambda) function we use the keyword, lambda.

That’s why the anonymous function is also called lambda function.

Syntax:

Example:

lambda arguments: expression
                

Few Points to Remember:

1. Lambda function can have any number of arguments, but only one expression.

2. The expression will be evaluated and return.

3. Lambda function cab be use anywhere, where the function object is required.

Example

Lambda function to square a number

square = lambda x : x * x
print(square(4))
print(square(5))
                

OUTPUT

16
25
                

In the above program, lambda x : x * x is lambda function, x is argument and x * x is expression.

square is a function pointer which points to the lambda function, and can use to call the lambda function.

The lambda function

square = lambda x : x * x
                    

is similar to

def square(x):
     return x * x
                    

OUTPUT

Hello from myfun
I accept one argument arg1 : Hello
                    

Use of Lambda Function:

Many built-in functions are available which takes argument as function( those are called higher order functions ), like map(), filter() reduce() etc.. in that case lambda function has the best use.

Use with filter()

The filter() function takes first argument as function and second argument as a sequence(like list).

The argument function will be called on every item of the sequence and return a new list, which contains items for which the function is evaluated to True.

Example

Example to filter only even numbers from a list

li = [1,2,5,12,16,8,10]

new_li = list(filter(lambda x: (x%2 == 0) , li))

print(new_li)
                

OUTPUT

[2,12,16,8,10]
                

Use with map()

The map() function takes first argument as function and second argument as list.

The argument function will be called on every item of the list and return a new list, which contains items for which the function is evaluated.

Example

Example to double all the numbers of a list

li = [1,2,5,12,16]

new_li = list(filter(lambda x: x * 2 , li))

print(new_li)
                

OUTPUT

[1, 4, 10, 24, 32]
                

Next chapter is Anonymous Function

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