Lambda Functions

Updated Oct 30, 2019 ·

Overview

Lambda functions are shorter and don't need a name. They are used for simple tasks where you don’t need to create a full function.

• Syntax: lambda arguments: expression
• You can use x for the argument, or any other name.
• The expression is like the function body.
• The result is automatically returned.

When to use Lambda:

• Lambda:
  • Use for simple tasks
  • When the function will only be used once
• Custom Functions:
  • Use for more complex logic
  • When the function will be reused many times

Using Lambda

If you only need to use the function once, you can directly define and call it with Lambda like this:

(lambda x: function(x))(x)

Example: To calculate the average, use sum(x)/len(x) as the function and pass the argument x.

## Computes the average of multiple values
(lambda x: sum(x)/len(x))([10, 20, 30])   # Output: 20.0

Storing Lambda

You can also store a lambda function in a variable and then call it like a regular function.

Example:

average = lambda x: sum(x) / len(x)
print(average([10, 20, 30]))  # Output: 20.0

Multiple Arguments

Lambda functions can take more than one argument.

Example: Raising one number to the power of another.

(lambda x, y: x ** y)(2,3) # Output: 8

Which could also be written as:

power = lambda x, y: x ** y
print(power(2, 3))  # Output: 8

Using Lambda with Iterables

Lambda functions work well with iterables, like lists. You can use them inside functions like map to modify every element and then convert to a data structure using the list function.

Example:

names = ['alice', 'bob', 'charlie']
capitalized_names = list(map(lambda x: x.capitalize(), names))
print(capitalized_names)  

Output:

['Alice', 'Bob', 'Charlie']

Calling Lambda In-Line

You can also define the function and print the output in one line.

Example: alculate the tax (20% of the sale price)

sale_price = 29.99

print((lambda x: x * 1.2)(sale_price)) ## Output: 35.988

If sale_price is a list of prices, you can use map to apply the tax calculation to each value, and list to convert the result into a list.

sales_prices = [29.99, 9.95, 14.50, 39.75, 60.00]

add_taxes = map(lambda x: x*1.2, sales_prices)
print(list(add_taxes))

Output:

[35.988, 11.94, 17.4, 47.699999999999996, 72.0]