# Python lambda (Anonymous Functions) | filter, map, reduce

In Python, anonymous function means that a function is without a name. As we already know that *def* keyword is used to define the normal functions and the *lambda* keyword is used to create anonymous functions. It has the following syntax:

lambda arguments: expression

- This function can have any number of arguments but only one expression, which is evaluated and returned.
- One is free to use lambda functions wherever function objects are required.
- You need to keep in your knowledge that lambda functions are syntactically restricted to a single expression.
- It has various uses in particular fields of programming besides other types of expressions in functions.

Let’s look at this example and try to understand the **difference between a normal def defined function and lambda function**. This is a program that returns the cube of a given value:

`# Python code to illustrate cube of a number ` `# showing difference between def() and lambda(). ` `def` `cube(y): ` ` ` `return` `y` `*` `y` `*` `y; ` ` ` `g ` `=` `lambda` `x: x` `*` `x` `*` `x ` `print` `(g(` `7` `)) ` ` ` `print` `(cube(` `5` `)) ` |

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*filter_none*

Output:

343 125

**Without using Lambda :**Here, both of them returns the cube of a given number. But, while using def, we needed to define a function with a name cube and needed to pass a value to it. After execution, we also needed to return the result from where the function was called using the*return*keyword.**Using Lambda :**Lambda definition does not include a “return” statement, it always contains an expression which is returned. We can also put a lambda definition anywhere a function is expected, and we don’t have to assign it to a variable at all. This is the simplicity of lambda functions.

Lambda functions can be used along with built-in functions like filter(), map() and reduce().

**Use of lambda() with filter()**

The filter() function in Python takes in a function and a list as arguments. This offers an elegant way to filter out all the elements of a sequence “sequence”, for which the function returns True. Here is a small program that returns the odd numbers from an input list:

`# Python code to illustrate ` `# filter() with lambda() ` `li ` `=` `[` `5` `, ` `7` `, ` `22` `, ` `97` `, ` `54` `, ` `62` `, ` `77` `, ` `23` `, ` `73` `, ` `61` `] ` `final_list ` `=` `list` `(` `filter` `(` `lambda` `x: (x` `%` `2` `!` `=` `0` `) , li)) ` `print` `(final_list) ` |

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*filter_none*

Output:

[5, 7, 97, 77, 23, 73, 61]

**Use of lambda() with map()**

The map() function in Python takes in a function and a list as argument. The function is called with a lambda function and a list and a new list is returned which contains all the lambda modified items returned by that function for each item. Example:

`# Python code to illustrate ` `# map() with lambda() ` `# to get double of a list. ` `li ` `=` `[` `5` `, ` `7` `, ` `22` `, ` `97` `, ` `54` `, ` `62` `, ` `77` `, ` `23` `, ` `73` `, ` `61` `] ` `final_list ` `=` `list` `(` `map` `(` `lambda` `x: x` `*` `2` `, li)) ` `print` `(final_list) ` |

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*filter_none*

Output:

[10, 14, 44, 194, 108, 124, 154, 46, 146, 122]

**Use of lambda() with reduce()**

The reduce() function in Python takes in a function and a list as argument. The function is called with a lambda function and a list and a new reduced result is returned. This performs a repetitive operation over the pairs of the list. This is a part of functools module. Example:

`# Python code to illustrate ` `# reduce() with lambda() ` `# to get sum of a list ` `from` `functools ` `import` `reduce` `li ` `=` `[` `5` `, ` `8` `, ` `10` `, ` `20` `, ` `50` `, ` `100` `] ` `sum` `=` `reduce` `((` `lambda` `x, y: x ` `+` `y), li) ` `print` `(` `sum` `) ` |

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*filter_none*

Output:

193

Here the results of previous two elements are added to the next element and this goes on till the end of the list like (((((5+8)+10)+20)+50)+100).

This article is contributed by **Chinmoy Lenka**. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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