Python Lambda

What are Python Lambda Functions?

Python Lambda functions are functions that do not have any name. Hence they are also known as anonymous or nameless functions. The word ‘lambda’ is a keyword. The function that follows the ‘lambda’ keyword is anonymous.

Functions Vs Lambda functions:

  • To define normal functions in function in Python, we use the ‘def’ keyword. We use ‘lambda’ keyword to define anonymous functions.
  • The lambda function can have any number of arguments, but they can return only one value in the form of expression. The Python lambda functions are syntactically restricted to a single expression.

Why use Python Lambda Functions?

  • Lambda functions come into the picture when we need a function only once.
  • Python Lambda functions are often used with built-in functions like filter(), map(), reduce(), etc.,
  • Using Lambda functions reduces the number of lines of code compared to normal functions.

Syntax:

lambda arguments:expression

As mentioned already, a lambda function can take any number of arguments but a single expression. Hence the number of arguments ranges from 0 to any number.

Examples:

With a single argument:

Here is an example to print the square root of a number.

a=lambda x:x**(1/2)
print(a(225))
15.0

x – is the argument.

x**(1/2) – The expression that gets evaluated.

lambda x:x**(1/2) – anonymous function which returns a function object.

>>> print(lambda x: x**(1/2))
<function <lambda> at 0x048388A0>

With multiple arguments:

Below is an example of a python lambda function that accepts multiple parameters.

a=lambda a,b,c:a+b+c
print(a(3,10,12))
25

When we write the same example using normal functions, which will take more lines. For instance,

def func(a,b,c):
    return a+b+c

print(func(3,10,12))

You might get this question, when we say lambda as nameless functions, then why we need to assign lambda function to some variable and call the lambda function using a variable. In general, we use lambda functions with higher-order functions and built-in functions like filter, map, reduce, etc.,

Lambda functions with normal functions:

def func(x):
    return lambda :x*x

a=func(4)
b=func(5)
print(a())
print(b())
16
25

In the above example, the function func() returns a lambda function. Whenever we call the func(), we make use of the lambda function.

lambda function with filter:

The filter function filters the iterable with the help of another function. The filter function takes the function to filter the iterable and iterable as an argument.

Syntax:

filter(function, iterable)

Example:

Let’s see an example to filter the even numbers from the list.

l=[7,4,9,2,3,8,5,12,10]
new_l=list(filter(lambda a:a%2==0,l))
print(new_l)
[4, 2, 8, 12, 10]

lambda function with map:

The map function applies a function to all the values in an iterable. The map function takes the function to be applied to the iterable and iterable as an argument.

Syntax:

map(function, iterable)

Example:

Get the even numbers from a list using the map function.

l=[12,14,3,9,15,25]
new_list = list(map(lambda x: (x%2 == 0), l))
print(new_list)
[True, True, False, False, False, False]

lambda function with reduce:

The reduce function applies a function to all the values of an iterable and returns a single number. The reduce function takes the function and iterable as an argument.

Syntax:

reduce(function, iterable)

Example:

Get the product of all the numbers in a list.

from functools import reduce

l=[12,14,3,9,15,25]
product=reduce((lambda x,y:x*y), l)
print(product)
1701000
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