What are lambda expressions in Python?

What are lambda expressions?

lambda expressions in Python are best described as single-use anonymous functions. What I mean by this, can be explained with a quick example.

[1,2,3,4,5]

I have this list of numbers that I want to square (multiply by itself). I could create a function like so.

def square(number):
    return number*number

This works fine, but what if you only need to do this one time? It would be a little cumbersome to have a function dedicated to this pretty menial task. We can use a lambda express for this instead.

lambda number: number*number

So you can see what's happening by referencing the above function next to our lambda expression. We declare lambda so the interpreter knows this is a lambda express. The first item is then the parameter which replaces the number argument in the square() function. Next is the actual result of the expression, number*number.

Here's an example using map() to get the squared result of each number in our list.

list(map(lambda number: number*number, numbers))
> [1,4,9,16,25]

I hope this is a good example to help you grasp lambda expressions so you can avoid huge pages of disposable functions!

Comments

[vuurball]

don't forget to pass the numbers to the map()

list(map(lambda number: number*number, numbers))

[Patrick Hanford]

Ah ha, good catch!

[Dustin]

Thank you, this was a good refresher from what I learned earlier in the year