Why use lambda functions?

user_134597 0
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I can find lots of stuff showing me what a lambda function is, and how the syntax works and what not. But other than the "coolness factor" (I can make a function in middle a call to another function, neat!) I haven't seen something that's overwelmingly compelling to say why I really need/want to use them.

It seems to be more of a stylistic or structual choice in most examples I've seen. And kinda breaks the "Only one correct way to do something" in python rule. How does it make my programs, more correct, more reliable, faster, or easier to understand? (Most coding standards I've seen tend to tell you to avoid overly complex statements on a single line. If it makes it easier to read break it up.)

lambda python
16 Answers

It is definitely true that abusing lambda functions often leads to bad and hard-to-read code. On the other hand, when used accurately, it does the opposite. There are already great answers in this thread, but one example I have come across is:

def power(n):
    return lambda x: x**n

square = power(2)
cubic = power(3)
quadruple = power(4)

print(square(10)) # 100
print(cubic(10)) # 1000
print(quadruple(10)) # 10000

This simplified case could be rewritten in many other ways without the use of lambda. Still, one can infer how lambda functions can increase readability and code reuse in perhaps more complex cases and functions with this example.

user_95954630

Lambdas are anonymous functions (function with no name) that can be assigned to a variable or that can be passed as an argument to another function. The usefulness of lambda will be realized when you need a small piece of function that will be run once in a while or just once. Instead of writing the function in global scope or including it as part of your main program you can toss around few lines of code when needed to a variable or another function. Also when you pass the function as an argument to another function during the function call you can change the argument (the anonymous function) making the function itself dynamic. Suppose if the anonymous function uses variables outside its scope it is called closure. This is useful in callback functions.

user_14453030

you master lambda, you master shortcuts in python.Here is why:

data=[(lambda x:x.text)(x.extract())  for x in soup.findAll('p') ]
                  ^1           ^2         ^3           ^4

here we can see 4 parts of the list comprehension:

  • 1: i finally want this
  • 2: x.extract will perform some operation on x, here it pop the element from soup
  • 3: x is the list iterable which is passed to the input of lambda at 2 along with extract operation
  • 4: some arbitary list

i had found no other way to use 2 statements in lambda, but with this kind of pipe-lining we can exploit the infinite potential of lambda.

Edit: as pointed out in the comments, by juanpa, its completely fine to use x.extract().text but the point was explaining the use of lambda pipe, ie passing the output of lambda1 as input to lambda2. via (lambda1 y:g(x))(lambda2 x:f(x))

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