Python `lambda` (anonymous) Functions

In this video, we learned to create and use lambda functions in Python with the help of examples.

Programs in the Video

Create Lambda Functions

Lambda functions are single-line functions defined without a name.

Let's first start with a simple function that takes in an argument and doubles it.

def double(n):
    return n * 2


print(double(10))

Output

Wouldn't it be neat if we could write this one-liner function in a more condensed way?

Python lambda functions allow us to do exactly that.

# def double(n):
#     return n * 2

double = lambda n: n * 2

print(double(10))

Output

The syntax of lambda function is:

lambda arguments: expression

Let's create one more lambda function to return the larger among two other numbers.

larger = lambda a, b: a if a > b else b

print(larger(10, 47))

Output

Suppose we have a list like this:

names = ['Alan', 'Gregory', 'Zlatan', 'Jonas', 'Tom', 'Augustine']

To sort this list alphabetically, we can use the list's sort() method.

names = ['Alan', 'Gregory', 'Zlatan', 'Jonas', 'Tom', 'Augustine']

names.sort()
print(names)

Output

['Alan', 'Augustine', 'Gregory', 'Jonas', 'Tom', 'Zlatan']

Instead of this, suppose we want to sort the items of this list based on the length of the name.

We can do this by passing an optional key argument to the sort() method.

names = ['Alan', 'Gregory', 'Zlatan', 'Jonas', 'Tom', 'Augustine']

names.sort(key=lambda x: len(x))
print(names)

Output

['Tom', 'Alan', 'Jonas', 'Zlatan', 'Gregory', 'Augustine']

Note: Lambda functions are used more frequently with Python builtin functions like map(), filter() and reduce.