Book Image

Functional Python Programming. - Second Edition

Book Image

Functional Python Programming. - Second Edition

Overview of this book

If you’re a Python developer who wants to discover how to take the power of functional programming (FP) and bring it into your own programs, then this book is essential for you, even if you know next to nothing about the paradigm. Starting with a general overview of functional concepts, you’ll explore common functional features such as first-class and higher-order functions, pure functions, and more. You’ll see how these are accomplished in Python 3.6 to give you the core foundations you’ll build upon. After that, you’ll discover common functional optimizations for Python to help your apps reach even higher speeds. You’ll learn FP concepts such as lazy evaluation using Python’s generator functions and expressions. Moving forward, you’ll learn to design and implement decorators to create composite functions. You'll also explore data preparation techniques and data exploration in depth, and see how the Python standard library fits the functional programming model. Finally, to top off your journey into the world of functional Python, you’ll at look at the PyMonad project and some larger examples to put everything into perspective.
Table of Contents (22 chapters)
Title Page
Packt Upsell
Contributors
Preface
Index

Reducing a product


In relational database theory, a join between tables can be thought of as a filtered product. A SQL SELECT statement that joins tables without a WHERE clause will produce a Cartesian product of rows in the tables. This can be thought of as the worst-case algorithm—a product without any filtering to pick the proper results. We can implement this using the itertools product() function to enumerate all possible combinations and filter those to keep the few that match properly.

We can define a join() function to join two iterable collections or generators, as shown in the following commands:

JT_ = TypeVar("JT_")
def join(
        t1: Iterable[JT_],
        t2: Iterable[JT_],
        where: Callable[[Tuple[JT_, JT_]], bool]
    ) -> Iterable[Tuple[JT_, JT_]]:
    return filter(where, product(t1, t2))

All combinations of the two iterables, t1 and t2, are computed. The filter() function will apply the given where() function to pass or reject two-tuples, hinted as Tuple[JT_, JT_...