Anonymous functions

One last type of functions that I want to talk about are anonymous functions. These functions, which are called lambdas in Python, are usually used when a fully-fledged function with its own name would be overkill, and all we want is a quick, simple one-liner that does the job.

Imagine that you want a list of all the numbers up to N that are multiples of five. Imagine that you want to filter those out using the filter function, which takes a function and an iterable and constructs a filter object that you can iterate on, from those elements of iterables for which the function returns True. Without using an anonymous function, you would do something like this:

# filter.regular.py
def is_multiple_of_five(n):
    return not n % 5

def get_multiples_of_five(n):
    return list(filter(is_multiple_of_five, range(n)))

Note how we use is_multiple_of_five to filter the first n natural numbers. This seems a bit excessive, the task is simple and we don't need to keep the is_multiple_of_five...