Built-in map, filter, and reduce — Python: Functions

All three higher-level functions we know are build-in in Python. However, map and filter are ready to use, and reduce must be imported from the functools module. Now, we will discuss the differences between each specific function and the simple options we implemented earlier.

The functools.reduce function

Looking at the function declaration, we see:

reduce(function, sequence[, initial]) -> value

Here it is worth paying attention to the fact that the initial value of the accumulator is an optional argument [, initial]. If it is not specified, then reduce will use the first element of the sequence as the initial value. In this case, we remember that the reduce call will result in an error if the sequence is empty.

Let us observe an example of the functools.reduce function:

from functools import reduce

numbers = [2, 3, 8]

def get_maximum(first_num, second_num):
    return first_num if first_num > second_num else second_num

reduce(get_maximum, numbers, 10)  # 10
reduce(get_maximum, numbers, 4)  # 8

The filter function

Now let us take a look at filter:

filter(function or None, iterable) -> filter object

Here is the code:

numbers = [2, 3, 8, 15, 34, 42]

def is_even(num):