Lambda expressions – also called “anonymous functions”.
Lambda expression #
Simple function:
def f(x):
return 2*x
f(2)
# 4
As a lambda expression:
lambda x: 2*x
We can assign it to a variable:
g = lambda x: 2*x
g(2)
# 4
Multiple inputs #
lambda x, y, z: <expression including x, y, z>
example:
full_name = lambda first_name, last_name: first_name.strip().title() + " " + last_name.strip().title()
full_name(" John", "smith ")
# John Smith
Reminder: strip() removes trailing white spaces, title() capitalizes
Lambda on a list #
Lambda functions can be applied to entire lists.
List functions sometimes have a key argument that can be populated with a lambda expression.
example:
list_of_full_names = [...]
# sort by surname
list_of_ful_names.sort(key = lambda name: name.split(" ")[-1])
Function to make functions #
# example from Socratica
def build_quadratic_function(a, b, c):
"""
return function f(x) = ax^2 + bx + c
"""
return lambda x: a*x**2 + b*x + c
f = build_quadratic_function(2, 3, -5)
f(0)
# -5
f(1)
# 0
# without naming the function
build_quadratic_function(2, 3, -5)(0)
# -5