Let's reach way, way back. 1989 - 1990. This will let me talk about OO programming and Python Type Hints. (really) And doing OO design for things that are as pervasive (and transparent) as air. Things that need to be part of a design, but don't appear in any documentation.

In …

I'll get to legacy software. First, however, some backstory on observability.

Sailors will sometimes create "Float Plans". Like aircraft flight plans, they have an itinerary to make it slightly easier to find us when something goes wrong. Unlike airspace, which is tightly controlled by the FAA, the seas are more-or-less …

The SOLID design principles beat the design boundary issue to death. Here are the principles in my preferred order. (See https://www.linkedin.com/learning/learning-s-o-l-i-d-programming-principles)

1. Interface Segregation -- minimize the boundaries. Do this first.
2. Liskov Substitution -- keep the boundaries consistent. Do this for hierarchies.
3. Open/Closed -- keep the boundaries stable …

Sometimes we call them "Belt and Braces" solutions. As a former suspenders person who switched to belts, the idea of wearing both is a little like over-engineering. In the unlikely event of catastrophic failure of one system, your pants can still remain properly hoist. There's a weird, but defensible reason …

I made some bad decisions when I wrote this a few years ago: https://github.com/slott56/Stingray-Reader. Really bad. And. Recently, I've burdened myself with conflicting goals. Ugh.

I need to upgrade to Python 3.8, and add type hints. This exposed somes badness.

See Stingray Reader Rewrite for …

Consider the following code

def max(m: int, n: int) -> int:
    if m >= n:
        return m
    elif n >= m:
        return n
    else:
        raise Exception(f"Design Error: {vars()}")

There's a question about else: clause and the exception raised there.

• It's impossible. In this specific case, a little algebra can provide …

See this

Dear Pythonista lazyweb: If I have a property spam and the attribute that backs it is _spam, what do we call that? The "backing attribute"? The "original property"? Something else? Is there an official term for this?

—Al Sweigart (@AlSweigart) January 29, 2019

My answer was -- frankly -- vague …

Read this. Goodbye, Object Oriented Programming I like this because parts of it are wrong, and parts are based on peculiarities of specific languages which aren’t problems in other languages.

The “wrong” things are on a spectrum. At one end are things almost right. The other end is hoped-for …