Functional Python Programming - Second Edition

Using reversed() to change the order

There are times when we need a sequence reversed. Python offers us two approaches to this: the reversed() function, and slices with reversed indices.

For example, consider performing a base conversion to hexadecimal or binary. The following code is a simple conversion function:

def digits(x: int, b: int) -> Iterator[int]:    if x == 0: return
    yield x % b
    for d in digits(x//b, b):
        yield d  

This function uses a recursion to yield the digits from the least significant to the most significant. The value of x%b will be the least significant digits of x in the base b.

We can formalize it as follows:

In many cases, ...