lambda-function

Python: What is a Lambda Function?

In Python ,the lambda keyword is used to define an anonymous(i.e.,nameless) function, using the follow syntax:

lambda parameters: expression

Assunme we have the follow list of fruits:

fruits = ['apple','orange','grape','lemon','mango','banana']

Now imagine we need to filter our list to print only fruit names which are 5 characters long.We could do so by defining a named function to test word lengths,and then passing it (and our list of fruits) to filter():

def five_letter_words(word):
    if len(word) == 5:
      return True
five_letter_fruits = filter(five_letter_words,fruits)

for fruit in five_letter_fruits:
  print(fruit)

Or, the same task can be accomeplished directly in filter() using lambda expression, without needing to define a separate named function:

five_letter_fruits = filter(lambda word:len(word)==5,fruits)
for fruit in five_letter_fruits:
  print(fruit)

Beacuse lambda functions are Python expressions, they can be assigned to variables.
So, this:

add_two = lambda x,y x+y
add_two(3,5)

Is equivalent to this:

def add_two(x,y):
  return x+y
add_two(3,5)