Why are Python lambdas useful? [closed]

Answer 1

lambda is just a fancy way of saying function. Other than its name, there is nothing obscure, intimidating or cryptic about it. When you read the following line, replace lambda by function in your mind:

>>> f = lambda x: x + 1
>>> f(3)
4

It just defines a function of x. Some other languages, like R, say it explicitly:

> f = function(x) { x + 1 }
> f(3)
4

You see? It's one of the most natural things to do in programming.

Answer 2

A lambda is part of a very important abstraction mechanism which deals with higher order functions. To get proper understanding of its value, please watch high quality lessons from Abelson and Sussman, and read the book SICP

These are relevant issues in modern software business, and becoming ever more popular.

Answer 3

I find lambda useful for a list of functions that do the same, but for different circumstances.

Like the Mozilla plural rules:

plural_rules = [
    lambda n: 'all',
    lambda n: 'singular' if n == 1 else 'plural',
    lambda n: 'singular' if 0 <= n <= 1 else 'plural',
    ...
]
# Call plural rule #1 with argument 4 to find out which sentence form to use.
plural_rule[1](4) # returns 'plural'

If you'd have to define a function for all of those you'd go mad by the end of it.
Also, it wouldn't be nice with function names like plural_rule_1, plural_rule_2, etc. And you'd need to eval() it when you're depending on a variable function id.

Answer 4

Pretty much anything you can do with lambda you can do better with either named functions or list and generator expressions.

Consequently, for the most part you should just one of those in basically any situation (except maybe for scratch code written in the interactive interpreter).

Answer 5

I use lambda to create callbacks that include parameters. It's cleaner writing a lambda in one line than to write a method to perform the same functionality.

For example:

import imported.module

def func():
    return lambda: imported.module.method("foo", "bar")

as opposed to:

import imported.module

def func():
    def cb():
        return imported.module.method("foo", "bar")
    return cb

Answer 6

Lambda is a procedure constructor. You can synthesize programs at run-time, although Python's lambda is not very powerful. Note that few people understand that kind of programming.