5.4. Lambda functions#

A lambda function, also known as an anonymous function is a small function consisting of a single expression. A lambda function is declared using

output = lambda arguments : expression

To demonstrate this lets declare lambda function to triple a number. Enter the following code into your program.

# Lambda functions
triple = lambda x : 3 * x

print()
print(triple(4))

Run your program and you should see the following added to the console.

12

5.4.1. Returning a lambda function#

Lambda functions can be used when we want to return a function from another function. For example, lets say that we want a function that multiples the input x by some number k. Enter the following into your program.

# Returning a lambda function
def multiply(k):
    return lambda x : k * x

We can then use the multiply() function to declare other functions to double, triple and quadruple the input. Enter the following into your program.

double = multiply(2)
triple = multiply(3)
quadruple = multiply(4)

print()
print(double(5))
print(triple(5))
print(quadruple(5))

Run your program and your should see the following added to the console.

10
15
20

5.4.2. Exercises#

Exercise 5.8

Write a lambda function that calculates the value \(y\) using the following quadratic for different input values of \(x\)

\[ y = 2x^2 - 3x + 4. \]

Use your function to calculate \(y\) when:

  1. \(x = 2\)

  2. \(x = 3\)

Exercise 5.9

Write a function called power_function() that returns a function which raises an input \(x\) to the power \(n\). Use this function to create the following functions:

  1. square() that calculates \(x^2\)

  2. cube() that calculates \(x^3\)

  3. quartic() that calculates \(x^4\)

Use your functions to calculate the square, cube and quartic of 123.