Tuesday, October 20, 2020

Type Hints to extend built-in structures

Working on revisions to a book. Fun stuff. See https://www.packtpub.com/product/python-3-object-oriented-programming/9781849511261 I may have the privilege of working with Dusty.

I've been using mypy for all my 2nd edition changes, but not in --strict mode. 

I've decided to ramp things up, and switch to strict type checking for all of the examples and case studies.

This lead me to stumble over

class MyThing(dict):
    def some_extra_method(self):

I absolutely could not get this to work for hours and hours.

I more-or-less gave up on it, until I started a similar example for a later chapter.

class ListWithFeatures(list):
    def feature(self):

This is almost the same, but, somehow, I understood it better.  As written, it is rejected by mypy. What I meant was this.

class ListWithFeatures(List[MyThing]):
    def __init__(self) -> None: ...
    def __init__(self, source: Iterable[MyThing]) -> None: ...
    def __init__(self, source: Optional[Iterable[MyThing]]) -> None:
        if source:
    def feature(self) -> float:
        return sum(thing.some_extra_method())/len(self)

I don't know why, but this was easier for me to visualize the problem.. It clarified my understanding profoundly.

We don't simply extend list or dict.  We should extend them because list is an alias for List[Any], and when being strict, we need to avoid Any. Aha.

Tuesday, October 13, 2020

Sources of Confusion: a "mea culpa" [Updated]

 I am not patient. I have been dismissed as one who does not suffer fools gladly.

This is a bad attitude, and I absolutely suffer from it. No denials here. I'm aware it limits my ability to help the deeply confused.

My personal failing is not being patient enough to discover the root cause of their confusion.

It's not that I don't care -- I would truly like to help them. It's that I can't keep my mouth shut while they explain their ridiculous chain of invalid assumptions as if things they invented have some tangible reality.

I'm old, and I'm not planning on becoming more empathetic. Instead, I've become less curious about wrong ideas. I find silence is helpful because I don't yell at them as much as I could.

Recently someone tried to tell me that a Python tuple wasn't **really** immutable. 


That's what they said.

A tuple of lists has lists that can be modified. (They did not have the courtesy to provide examples, I've had to add examples based I what I assume they're talking about.)

>>> t = ([], [], [])
>>> t[0].append(42)
>>> t
([42]. [], [])

"See," they said. "Mutable." 

Implicit follow-up: Python is a web of lies and there's no reason for it to be better than a spreadsheet.

I did not ask how the immutability of a tuple was magically transferred to the lists contained within the tuple. 

I did not ask about their infections disease theory of protocol transformation of types. Somehow, when associated with a tuple, the list became tuple-like, and lost a bunch of methods. 

I did not ask if they thought there was some some method-shedding feature where an immutable structure forces other data structures to shed methods.

I did not ask what was supposed to happen to a dictionary, where there's no built-in frozen dictionary.

I did not ask what would happen with a "custom" class (one created in the app, not a built-in collection.)

I did not ask what fantasy land they come from where a tuple of mutable objects would lead to immutability of the contained objects.

I did not ask if it worked the other way, too: was a list of tuples also supposed to freeze up? 

I did not ask if it transferred more than one level deep into the lists inside the tuple.

I should have.

It was an epic failing on my part to not dig into the bizzaro world where the question could arise.

BTW. They had the same complaint about frozen data classes. (Again. They did not have the courtesy to provide code. I'm guessing this is what they meant. My failure for not asking.)

>>> from typing import List
>>> from dataclasses import dataclass
>>> @dataclass(frozen=True)
... class Kidding_Right:
...     one_thing: List[int]
...     another_thing: List[int]
>>> kr = Kidding_Right([], [])
>>> kr.one_thing.append(42)
>>> kr
Kidding_Right(one_thing=[42], another_thing=[])

Triumphant Sneer: "See, frozen is little more than a suggestion. The lists within the data class are *not* frozen." 

Yes. They appeared to be claiming frozen was supposed to apply transitively to the objects within the dataclass.  Appeared. My mistake was failing to ask what they hell they were talking about.

I really couldn't bear to know what caused someone to think this was in any way "confusing" or required "clarification." I didn't want to hear about transitivity and how the data class properties were supposed to infect the underlying objects. 

Their notion was essentially wrong, and wickedly so. I could have asked, but I'm not sure I could have waited patiently through their answer.


"little more than a suggestion".


This is an strange confusion.

A dynamic language (like Python) resolves everything at run-time. It turns out that there are ways to override __getattr__() and __setattr__() to break the frozen setting. Indeed, you can reach into the internal __dict__ object and do real damage to the object.

I guess the consequences of a dynamic language can be confusing if you aren't expecting a dynamic language to actually be dynamic.

Tuesday, October 6, 2020

The Python Podcast __init__

Check out https://www.pythonpodcast.com/steven-lott-learn-to-code-episode-283/. This was a fun conversation on Python and learning.

We didn't talk about my books in detail. Instead, we talked about learning and what it takes to get closer to mastery.

It's a thing I worry about. I suspect other writers worry about it, also. Will the reader take the next steps? Or will they simply think they've got it because the read about it?

Wednesday, September 9, 2020

Open Source Support Ideas

"... [I] am thinking of building an in house conda forge, or buying a solution, or paying someone to set something up."

The build v. Buy decision. This is always hard. Really hard.  

We used to ask "What's your business? Is it building software or making widgets?" 

And (for some) the business is making widgets.

This is short-sighted. 

But. A lot of folks in senior positions were given this as a model back in the olden days. So, you need to address the "how much non-widget stuff are we going to take on?" question.

The "Our Business is Widgets" is short-sighted because it fails to recognize where the money is made. It's the ancillary things *around* the widgets. Things only software can do. Customer satisfaction. Supply-chain management. 

So. Business development == Software development. They're inextricably bound.

With that background, lets' look at what you want to do.

Open Source software is not actually "free" in any sense. Someone has to support it. If you embrace open source, then, you have to support it in-house. Somehow. And that in-house work isn't small.  

The in-house open-source support comes in degrees, starting with a distant "throw money at a maintainer" kind of action. You know. Support NumFocus and Anaconda and hope it trickles down appropriately (it  sometimes does) to the real maintainers.  

The next step is to build the tooling (and expertise) in-house. Conda forge (or maybe JFrog or something else) and have someone on staff who can grow to really understand how it fits together. They may not be up to external contributions, but they can do the installs, make sure things are running, handle updates, manage certificates, rotate keys, all the things that lead to smooth experience for users.  

The top step is to hire one of the principles and let them do their open source thing but give them office space and a salary.  

I'm big on the middle step. Do it in-house. It's *not* your core business (in a very narrow, legal and finance sense) but it *is* the backbone fo the information-centric value-add where the real money is made.  

Folks in management (usually accouting) get frustrated with this approach. It seems like it should take a month or two and you're up and running. (The GAAP requires we plan like this. Make up a random date. Make up a random budget.)

But. Then. 13 weeks into the 8-week project, you still don't have a reliable, high-performance server.  Accounting gets grumpy because the plan you have them months ago turns out to have been riddled with invalid assumptions and half-truths. (They get revenge by cancelling the project at the worst moment to be sure it's a huge loss in everyone's eyes.)

I think the mistake is failing to enumerate the lessons learned. A lot will be learned. A real lot. And some of it is small, but it still takes all day to figure it out. Other things are big and take failed roll-outs and screwed up backup-restore activities. It's essential to make a strong parallel between open source and open learning.

You don't know everything. (Indeed, you can't, much to the consternation of the accountants.) But. You are learning at a steady rate. The money is creating significant value. 

And after 26 weeks, when things *really* seem to be working, there needs to be a very splashy list of "things we can do now that we couldn't do before."  A demo of starting a new project. `conda create demo python=3.8.6 --file demo_env.yml` and watch it run, baby. A little dask. Maybe analyze some taxicab data.

Tuesday, September 1, 2020

A Comprehensive Introduction to Python

Python 101, by Michael Driscoll. 545 pages, available from leanpub.com in a variety of formats. Available soon in hardcover.

The modern Python programming language is a large topic. A book on a programming language has to be seen as a collection of several large topics.

At its core, a book on a programming language has to cover the syntax of the language. What’s for more important is covering the underlying semantics of the various constructs. Software captures knowledge, and it’s essential for a book on a programming language to make it clear how the language expresses knowledge.

For a programming expert, a fifteen page technical report can be enough to get started with a new language. When I was first learning to program, that’s all there was. For the vast majority of people who come in contact with programming, there’s a lot more information required.

This leads to a number of interesting tradeoffs when writing about a programming language. How much of a book should be devoted to installing the language tools? How much should it cover the other tools required to create software? I think Python 101 makes good choices.

In the modern era of open-source software, the volume and sophistication of the available tools can be daunting. An author must consider how many words to invest in text editors, debuggers, performance measurement, testing, and documentation. These are all important parts of producing software, they’re often tied closely with a language, but these additional tools aren’t really the language itself.

A language like Python offers a rich collection of built-in data types. A book’s essential job is to cover the data structures (and algorithms) that are first-class parts of the Python language. A focus on data puts the various syntactic elements (like statements) into perspective. The break statement, for example, can’t really be discussed in isolation. It’s part of the conversation about for statements and conditional processing in if statements. Because Python 101 follows this data-first approach, I think it can help build comprehensive Python skills.

The coverage of built-in data structures in a modern language needs to include file objects. While Python reads strings and bytes, the standard library provides ways to read HTML, CSV, JSON, and XML documents. Additional packages provide access to Excel spreadsheet files. While, technically, not part of the language, these are essential parts of the problem domain a programming language like Python is designed to address. Because these are part of the book, a reader will be empowered to solve practical problems.

There was a time when a programming “paradigm” was part of a book’s theme. Functional programming, procedural programming, and object-oriented programming approaches spawned their own libraries. Some languages have a strong bias. Other languages, like Python, lack a strong bias. A developer can work with functions, using material from the first seventeen chapters of Python 101 and be happy and successful. Moving into class definitions can be helpful for simplifying certain kinds of programs, but it’s not required, and a good book on Python should treat classes as a sensible alternative to functions for handling more complex object state and bundle operations with the state.

Moving beyond the language itself, a book can only pick a few topics that can be called “advanced.” This book looks at some of the language internals, exposed via introspection. It touches on some of the standard library modules for managing subprocesses and threads. It covers tools like debuggers and profilers. It expands to cover development environments like the Jupyter Notebook, also. I’d prefer to reduce coverage of threading and switch to Jupyter Lab from Jupyter Notebook. These are small changes at the edges of large pool of important details.

I’m still waffling over one choice of advanced topics. Does unit testing count as an advanced topic? For software professionals, a testing framework is as important as the language itself. For amateur hackers, however, a testing framework may be a more advanced topic. The location of a chapter on unit testing is a telling indication of who the book’s audience is. 

The Python ecosystem includes the standard library and the vast collection of packages and applications available through the Python Package Index. These components can all be added to a Python environment. This means any book on the language must also cover parts of the standard library, as well as covering how to install  new packages from the larger ecosystem. Python 101 doesn’t disappoint. There are solid chapters in PIP and Virtual Environment management. I can quibble over their  place in Part II. The presence of chapters on tools is important; Python is more than a language; Python 101 makes it clear Python is a collection of tools for building on the work of others to solve problems collaboratively.

I’m not easily convinced that Part IV has the same focus on helping the new programmer as the earlier three parts. I think packaging and distribution considerations take the reader too far outside problem-solving with a programming language and tools. I’m not sure the audience who sees testing as an advanced topic is ready to distribute their code. I think there’s room for a Python 102 book to cover these more professionally-oriented topics.

The volume of material covered by this comprehensive book on Python seems to require something more elaborate than a simple, linear sequence of chapters. The sequence of chapters have jumps that seem a little awkward. For example, from an introduction run-time introduction introspection, we move to the PIP and virtual environment tools, then move back to ways to make best use of Python’s annotations and type hints. Calling this flow awkward is — admittedly — a highly nuanced consideration. I suspect few people will read this book sequentially; when each chapter is used more-or-less independently, the sequence of chapters becomes a minor side-bar consideration. Each chapter has generous examples and there are screen shots where necessary. 

The scope of this book covers the language and the features through Python 3.8 in a complete and intelligible way. The depth is appropriate for a beginning audience and the examples are focused on simple, concrete, easy-to-understand code. The presence of review questions in each chapter is a delight, making it easy to leverage the book for instructor-guided training. I can imagine covering a few chapters each week and quizzing students with the review questions. Some of the questions are nicely advanced and can lead to further exploration of the language.

If you’re new to Python, this should be part of your Python reading list. If you’ve just started and need more examples and help in using some of the common tools, this book will be very helpful. If you’re teaching or helping guide people deeper into Python, this may be a helpful resource. 

Driscoll’s colorful nature photos are a bonus. My Kindle is limited to black and white, and the pictures would have been disappointing. I’m glad I got the PDF version.

Tuesday, August 25, 2020

Another shiny new MacBook pro

See https://slott-softwarearchitect.blogspot.com/2014/03/shiny-new-macbook-pro.html

At the time (2014), the 8Gb machine was way more than adequate for all my needs as a writer.

Enter bloat.

Mac OS Catalina has essentially filled this machine to the breaking point. Six short years is the lifespan. Things (generally) work, but it now crashes frequently. Sometimes, streaming TV won't play properly. I've tried a large number of remedies (reboot WiFi, reboot computer, reset Bluetooth) and it glitches too offten to be comfortable.

(Rumors suggest the crashes seem to be associated with going to sleep. The machine crashes when it's idle. I come back to it and find it has restarted, and needs to restart my apps. It's not horrible. But it's an indication of a deeper problem. And it's time.)

It works. But. I've spent too many years waiting for slow computers and slow networks. An hour a day (cumulative) for 300 days a year for 40 years means I've spent 1.3 years of my life waiting for a computer to do something.

I’m reluctantly replacing my kind-of-working "Late 2013" vintage machine with a new 13” MacBook Pro. At least 16Gb RAM. At least a terabyte of storage. Hopefully, things will not be "glitchy" and I won't have constant crashes.

I’ve gotten used to having an 27" Thunderbolt Display, and a USB Querkywriter keyboard, and two USB disks doing backups. That's a lot of stuff plugged in all the time. Also. I really need a slot for SD cards (the boat uses micro SD cards, as does the old GoPro camera.). So. A fancy USB-C hub will be essential, I think.

The question is 2 ports (power and hub) or 4 ports (power, hub, and two other things)?  I suspect I can live with 2 ports.  4 ports ships immediately.

I have several use cases:
Writing books actually requires some computing power. But. Not *too* much power. The general reader doesn’t always have a huge computer. If my examples require more computing power than my readers have access to, that’s a problem. The advantage of having a smallish computer is I’m not overstepping what’s available to my readers. This is a handy way to take a tax deduction to pay for this extravagance.

Writing fiction requires a small machine. Scrivener works on an iPad Pro. I’m good with almost anything. Even an iPhone can be used for writing and editing fiction. It’s hard, of course, with a tiny screen. But not impossible. And. I'm trying to learn the craft, so tools aren't as important as understanding character arc.

Creating MicroPython-based devices is a bit confusing right now. A lot of the development environments depend on a reliable USB connectivity to the Arduino or Circuit Playground Express board. I worry about the (potential) complexity of introducing a USB hub into the mix.  I suspect I only need to replace some of my USB cables; the Arduino boards all seem to use a bulky USB type B. The CPX use USB type Micro B. (I thinks one can be replaced with a USB C to USB B “printer cable”, the other is a USB microB to C adapter. Or, maybe a USB C to USB A adapter can be used with my vast collection of legacy cables. Don't know.)

Boating involves connecting external devices like the GPS antenna to the laptop and tracking position or planning routes. This is a Bluetooth thing, generally. 

It does require considerable power for the laptop; the 60W power brick becomes a constraint. The boat have an inverter and can handle the load gracefully. A computer is a dedicated 5A draw, though; twice what the fridge pulls (and the fridge runs infrequently.) We have 225Ah available. The computer could be as bad as 120Ah if it was left on for 24 hours during an overnight passage.

The good news is that the use cases are more-or-less exclusive. The boating use case is rare. We have more thrifty navigation systems permanently installed on the boat. Many folks are using CPX and Arduino’s with MacBook Pro’s, so I shouldn’t worry too much, just buy new cables.

The best part?

Since I use Time Machine, the new machine recovers from the Time Machine backups. It has to be left to run overnight, but. Boom. Done.

(On the to-do list -- encrypt the backup volumes. Ugh. But. Necessary.)