fidzu : python

Once again this month the community put most of its energy into fixing bugs, refining existing behaviour, and improving performance on top of our last LTS release 8.0. In addition, we are happy to present a selection of new features and documentation updates in this newsletter.

For an in depth overview of the Tryton issues please take a look at our issue tracker or see the issues and merge requests filtered by label.

Changes for the User

Sales, Purchases and Projects

We now move the warehouse and the shipping date of the sale to a different page, which keeps the sale form a little more compact.

Accounting, Invoicing and Payments

The entry for invoice payment methods is now moved under the invoice payments menu, so the menus for invoices and invoice payments are no longer mixed.

Accounts with the setting party required are now grouping their account move lines per party in the general ledger.

The lines of the general ledger account are now ordered consistently with the cumulative balance.

We update the version of Stripe used by the payment gateway to the latest one.

Stock, Production and Shipments

On the stock move form, the cost fields are now displayed more cleanly: the commission price is only shown when it is set.

User Interface

The binary and image widgets now accept a custom filters attribute, so administrators can restrict the file types users see when picking or saving a file.

When downloading a product image, the file is now suffixed with the proper .jpg extension, which makes the file easier to open from a folder.

For tall screens, the maximal height of tree views and list forms is now relative to the viewport instead of a fixed pixel value, so the available vertical space is no longer wasted.

In the domain parser, selection values are now completed using a "contains" matcher instead of "starts with", which makes it easier to write a filter when several options share a common prefix.

Searching by record name on a contact mechanism now also matches the contact mechanism's own name field, so users can find a phone number or e-mail by typing a label like "office" or "personal".

New Documentation

The help text of the tax rule fields on the party is now explicit about what happens when the field is left empty.

The usage of the active_test context key in ModelSQL.search_domain is now documented in the reference manual.

The module tutorial has been updated to match the layout of the project skeleton generated by cookiecutter, so newcomers can follow it without surprises.

New Releases

We released bug fixes for the currently maintained long term support series
8.0 and 7.0, and for the penultimate series 7.8.

Changes for Implementers and Developers

The WSGI dispatcher now handles exceptions raised from within the with_pool decorator itself: unexpected exceptions are logged at exception level and their traceback is written to the WSGI wsgi.errors stream, while exceptions used as HTTP responses have their description converted to a plain string.

This text is produced by utilising minimax-m3.

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01 Jul 2026 8:30am GMT

With the recent approval of PEP 772 - Packaging Council governance process, a new Python Packaging Council (PPC) is being established with broad authority over packaging specifications and the mandate to coordinate Python packaging efforts. The election of the inaugural PPC will be held in parallel to the 2026 Python Software Foundation (PSF) Board election.

What is the Python Packaging Council?

The PPC will be the technical decision making body for the interoperability specifications affecting how Python packages are built, distributed, and installed.

The council will also serve as a coordinating body for the Python packaging ecosystem, working with many stakeholders from the wider Python community toward an ever-improving packaging user experience. This will include the maintainers of various packaging tools like the Python Packaging Authority (PyPA), the Python core team, the Python Steering Council, and the PSF.

Election Overview

The 2026 inaugural election fills all five seats on the PPC. The two candidates receiving the highest number of votes shall be designated Cohort A with a two-year term, and the three candidates receiving the next highest number of votes shall be designated Cohort B with a one-year term.

In future elections, each cohort will be elected for a full two-year term in alternating years, so that roughly half of the PPC turns over each cycle.

Election Timeline

The PPC election follows the same timeline as the PSF Board election:

• Nominations open: Tuesday, July 28th, 2:00 pm UTC

• Nomination cut-off: Tuesday, August 11th, 2:00 pm UTC

• Announce candidates: Thursday, August 13th

• Voter affirmation cut-off: Tuesday, August 25th, 2:00 pm UTC

• Voting start date: Tuesday, September 1st, 2:00 pm UTC

• Voting end date: Tuesday, September 15th, 2:00 pm UTC

Voting

You must be a Contributing, Supporting, or Fellow member by August 25th and affirm your intention to vote to participate in this election.

Check out the PSF membership page to learn more about membership classes and benefits. You can affirm your voting intention by following the steps in the PSF's video tutorial:

• Log in to psfmember.org

• Choose "Your Memberships" page at the top right to check your eligibility to vote (You must be a Contributing, Supporting, or Fellow member)

• Choose "Voting Affirmation" page at the top right

• Select your preferred intention for voting in 2026 (which now includes a second affirmation regarding your intention to vote in the PPC election)

• Click the "Submit" button

Like the PSF Board elections, casting a vote in a PPC election will automatically affirm your intention to participate in the next PPC election.

If you have questions about membership, please email pc-elections@python.org.

Election communications from psfmember.org

PSF Members should review their communication preferences on psfmember.org if you would like to opt in or out of receiving emails about the PSF Board, PPC elections, or both. Here's how:

• Log in to psfmember.org

• Navigate to your "Profile" page

• Click the "Name and Address" tab

• Scroll down, designate your preferences

• Click submit

If you had previously opted out of communications from the PSF through psfmember.org and would like to review or change your preference, we encourage you to update them using the instructions above. The PSF only sends a handful of election and fundraising related communications every year via psfmember.org.

Running for the Packaging Council

Do you have a vision for improving the Python packaging experience? Do you make the tools used to build and consume Python packages? Are you passionate about building communities, consensus, and standards focused on the user experience? If these resonate with you, and you have the time to attend regular meetings and participate in the standardization process, you should consider running for the inaugural PPC!

We're looking for candidates who can build bridges between projects and communities, who enjoy working with a very large community of passionate volunteers, and have a willingness to represent the wider community ahead of any single tool, project, or employer. We also welcome candidates who have a diverse set of skills and experiences, including open-governance experience, community stewardship, fundraising knowledge, and (of course!) technical expertise in Python packaging and distribution.

PEP 772 does provide non-binding operational suggestions, which hint at how the council could function. As this is the inaugural PPC, the individuals serving on it will be establishing the initial operating procedures, scope, interests, and agenda that future councils will build upon. Notably, "establishing specific processes for [the] Packaging Council and PyPA relationship" is something that the inaugural Packaging Council is expected to do.

You can nominate yourself or someone else. If you're nominating someone else, we'd encourage you to reach out to them first to make sure they're excited about the opportunity and give them a heads up that they'll need to submit their own nomination statement too. Nominations open on Tuesday, July 28th, 2:00 pm UTC, so you have time to talk with potential nominees, research the role, and craft a nomination statement for yourself or others. Remember, nominees must themselves be PSF voting members, and nomination statements must include information about the nominee's relevant affiliations.

01 Jul 2026 7:57am GMT

CRA, EU Cyber Resilience Act, has stirred a lot of discussion in the Open Source Communities. Will my project be usable in EU anymore? What are my responsibilities as a developer of open source software? My software is shipped with a commercial software, does it make me a manufacturer? Open Source Community is dealing with a lot of confusion and qurries relating to EU Cyber Resilience Act. I am no different especially the deadline coming in next few months.

Red Hat has formally identified with the role of Open Source Steward for Ansible project. We, at Ansible community divided the complaince jounry in the following 4 phases :

• Gap analysis
• Implementation
• Communication
• Plan the next phase

Gap analysis

Finding out

• What does the law says?
• Requirement to be CRA compliant (for the role of steward)
• What does it mean to CRA steward compliant for Ansible project?
• Find out the gaps under CRA in the Ansible project

Implemention

The next phase for Ansible is implementation.
CRA should be viewed by the lenses of security. An opportunity to make the project secure by default and not the afterthought. With these intent earlier this year I, posted in Ansible Forum

• EU Cyber Resilience Act (CRA) and what it means for Ansible?
• Security as Default, Not an Afterthought: The CRA&aposs Real Message

As part of this work (as a member of the Ansible community and PE engineering team at Red Hat), we filed the following PRs to be reviewed by the community :

1. vulnerability management policy PR
2. security best practices PR
3. security policy PR

In the coming weeks and months you will read more on this topic from me.

30 Jun 2026 8:18pm GMT

I once needed the SLA for an endpoint my dashboard leaned on, so I asked the team that owned it. Their lead came back with 200ms ± 500ms. Read that literally and the fastest responses arrive 300ms before the request is even sent. The number wasn't malicious - it came straight out of the standard formulas. The formulas were wrong for the data, and that mistake is everywhere.

30 Jun 2026 10:00am GMT

Maintaining a mature, reasonably-popular Django open-source is boring. Here I explore using a LLM to automate away some of the boring work.

28 Jun 2026 3:00am GMT

I recently attended my first PG Data 2026 conference where keynote speaker Robert Haas delivered a talk that has stayed with me. His keynote focused on the people behind PostgreSQL, the growing challenges of sustaining open-source communities, and the urgent need to cultivate new contributors through mentorship and community engagement. While his remarks centered on PostgreSQL, they sparked broader reflections for me about the future of open source and communities like Django.

26 Jun 2026 7:00pm GMT

As I have discussed in previous posts, "AIs" can make mistakes. In fact, they do make mistakes, and their mistake-making patterns are such that where and how they will make mistakes is both uncertain and constantly changing.

Thus, in any scenario where you want to attempt to make "productive" use of "AI", you must have a system in place for checking every result. Not checking some results; checking every result. If each result might have a consequence for you (and if it didn't have a consequence, why bother automating it?) and you cannot predict in advance which kinds of results will need verification, then verification is always required.

The verification often ends up being just as expensive as doing the work in the first place, which means that if you want your usage of "AI" to be personally profitable, you have to find someone else to externalize the cost of verification onto. This person becomes your adversary, and, if you are successful, your "AI's" victim.

The Ladder-Climber And Their Reverse-Centaur Rungs

One way that this constellation of facts can straightforwardly assemble themselves into a dystopian nightmare is the phenomenon, described by Cory Doctorow, of the reverse centaur. This is when your employer non-consensually turns you into the verification system. The "AI" does the fun part of initially performing the work, and then you do the boring part where you check if the robot is right and clean up its messes, even if everyone already knows that it would, in aggregate, be cheaper for you to do the work in the first place.

Reverse centaurs can be made from any automation, not only "AI" automation. I think that there is a reason that this term happens to have emerged in the "age of AI", though, and not with earlier automation technologies (even those which were considerably more viscerally horrific). That reason is: the wrongness of "AI" output is not merely a technical feature that must be compensated for, it is a generalized externality.

As I mentioned above, if you are responsible for the entirety of the work, both extruding the "AI" output and checking it, it's usually cheaper to have humans do the entirety of the work to begin with. When humans do the writing directly, we can check as we go, and thus verification doesn't need to be as comprehensive.

When "AI" coding advocates say "code review is the bottleneck", what they are observing is that the LLM is still rolling the dice for each PR, and a human is still necessary to verify that each of those rolls is a winner. But calling this process "code review" is a bit of a misnomer; it's not really "code review" in the traditional sense, it's human understanding.

Before the advent of "AI", the human understanding was implicit in the process of writing the code in the first place¹, and the code review was a way of diffusing and extending that understanding. Now that the code can be authored with no initial understanding taking place, that cost has not gone away, it has moved.

Human understanding was always the bottleneck.

However, this is taking a collaborative view of a software project, where satisfying the needs and solving the problems of your customers are the goals. We can see that "AI" is a bad tool to satisfy those goals, because all it's doing is converting the first half of the work, that of understanding the code as you write it, to understanding the agent's output as you read it.

What if, instead, we were to take the view that every software company is a Hobbesian nightmare, red in tooth and claw? In this view, the only goal of a software project is for the individual developers to make their promo cycles and get their bonuses. Given that there is only a certain amount of money to go around, this is a zero-sum game where each programmer wants to look more productive than their colleagues.

Pretty much every organization finds it easy to reward "productivity" as expressed by lines of code emitted, but the benefits of doing thorough and thoughtful design, analysis, and code review very difficult to reward. In this world, an LLM is an invaluable tool for the sociopathic ladder-climber, particularly if your legacy organization is still structuring their workflows as if the person prompting the bot is "writing" the code, and then they get to foist off the act of "reviewing" the code onto someone else.

Here, the prompter effectively externalizes the cost of the LLM's failures but internalizes any benefits. The prompter will vibe-code a big feature, so large that the assigned reviewer can't possibly comprehend it all effectively. When this happens, the reviewer will, eventually, be pressured to approve it, even if they can try to spot a few problems along the way. The reviewer has their own work to get back to, after all, the obligation to review the prompter's (read: the bot's) code is a drain on their time that they are not going to get rewarded for.

If this feature is a big success, the prompter gets a promotion. If it causes a big issue, well, the reviewer must not have been careful enough.

This is why LLMs are "good for coding", and also why their biggest promoters keep having outages.

The Generative Gish Galloper

Coding is the biggest "success story" of this type of adversarial communication, but it is by far not the only instance of such a thing. LLMs create a new form of leverage that can turn Brandolini's law from a linear advantage into an exponential one. If you are engaged in a political debate where you want to overwhelm the other side in nonsense, an LLM can generate bullshit faster than it is physically possible for a human being to type, let alone respond thoughtfully. There is an asymmetry to the utility of this weapon as well: only one side of the political spectrum wants to flood the zone and destroy trust in institutions and the concept of truth. There's a good reason that the fascists love it.

Straightforward Spam and Fraud

This is kind of obvious, but LLMs can generate lightly-customized, plausible-looking text much more quickly than any human being. This facilitates their use in fraud, spam, and scams. In a spamming or fraudulent interaction, once again, the costs are externalized onto the victim: the recipient of a spam message has to do all the work of "checking" the LLM's output. Spammers already expect very low hit rates from boilerplate, and if the LLM can increase those percentages from 1% to 5% the technology will pay for itself; they don't need anything like reliable accuracy.

Customer "Support"

If you have any kind of commercial relationship with a company, I probably don't even need to mention this: customer "support" bots are a misery. Everybody knows it at this point. But customer support is usually conceptualized by businesses as an adversarial interaction, because it is a cost center. They maintain internal metrics on time-to-resolution and try to optimize them. Implicitly, this creates a dynamic where the goal of the customer service agent's job is not to solve your problem, but to emit noise that will cause you to think your problem is resolved, or to give up, as fast as possible. Unsurprisingly, LLMs can emit this noise faster than humans can, getting those customers off the phone. But those customers will remember those interactions, and the story outside the TTR metrics is horrible.

Similarly to the situation in software development, LLMs can look very good on paper for customer support, but mostly what they are doing is illuminating the problems with the industry's existing metrics, by turning "winning the metrics battle against the customer" into a more obvious and immediate defeat for the company's long term reputation.

"Education"

In 2026 it is sadly a fact of life that students cheat all the time using "AI", and that this cheating is very successful, in that the teachers find it very hard to detect.

LLMs are great for cheating on schoolwork because the student is externalizing the work of the checking onto the teachers, who are often starting at a disadvantage to begin with, at least in the US.

My view is that this is happening because of a divergence in the way that students vs. teachers (or, more accurately, "the broader educational system") view grading.

When a student is asked to write an essay, the teachers see the effort as both intrinsically worthwhile for the student, as well as useful as a pedagogical tool to evaluate and react to the student's progress. The student, by contrast, sees a stumbling block designed to knock them off the path to success and into a permanent underclass. It is no wonder that the student sees "AI" as useful to their own goals and has no compunction about deploying it.

There is a bitter irony that the ability to understand the inherent value of actually writing the essay on their own is the sort of thing that students can really only learn by writing a bunch of essays. There's no way that I can think of which makes the benefit legible as long as a shortcut is available.

The net effect here is a downward spiral, where the already-wobbling educational system is sustaining an attack that it doesn't have the resources to recover from. The individual students' attacks against their teachers and their schools' grading systems might appear to momentarily succeed, but they will win the battle and lose the war.

Spamming "For Good"?

Usually when we talk about someone unilaterally choosing to enter into an adversarial relationship, that's an "attack" and for good reasons we have a negative impression of the attacker. However, I would be remiss if I did not point out that there are some cases where the relationship was already adversarial; just because you're the attacker doesn't mean that you are evil.

For example we might imagine use-cases like automatically filing appeals for prior authorizations against health insurance. It's relatively well-known at this point that the main way for-profit insurers maintain their margins is by denying claims right up to the line of the policies themselves being fraud, so using a spamming tool to fight them might be entirely justifiable² in that case.

Similarly, using an LLM could be justified in a fight against a company refusing to honor a warranty. One could imagine using an LLM to immediately generate replies and escalations.

However, even in imagined cases like these, the underlying problem is that the insurers and the vendors already have a tremendous amount of structural power, so it is more likely that they will have the advantage in deploying a communications weapon like an LLM, as well as enacting policies to simply ignore any LLM-based communication that you might submit. Worse, if these strategies were to become widespread, they might provide an excuse to reject any communications by feeding them into an unreliable "LLM detector" and issuing an automated "computer says no" even to hand-written correspondence.

It is also worth stressing that these cases are imagined, as compared to the very real coworker-abuse, spam, scam, fraud, and disinformation campaigns being waged in real life today.

Therefore, while legitimate uses might exist, it's hard to imagine that there's anywhere they would be genuinely valuable and sustainable. In the best case "AI" will provide a temporary advantage for underdogs that will provoke an arms race which the resource-advantaged adversaries will win in the long run, in the worst case the arms race itself will cement permanent structural change that will make things worse.

"Search" By Stealing

Most of the adversarial utility of "AI" is on the "write" side, since write-amplification is more obviously aggressive than reading. But the "read" side of LLMs - summarization and question-answering - can be a form of attack as well.

To begin with, the act of reading itself is currently enormously destructive, but that's arguably not a fundamental aspect of this technology. They could set reasonable rate-limits and respect things like robots.txt, as search engines have for decades now. They could also refrain from committing criminal levels of copyright infringement. But, today, using "AI" tools does suborn this sort of out-of-control crawling.

More insidiously, consider the scenario described in this YouTube video. The LTT Bros decided to try Linux again, and in the course of so doing, they had problems. When trying to solve these problems, they were faced with a choice: they could consult Reddit, or they could ask an LLM. Asking an LLM would "gaslight the heck out of" them, but they still found it preferable, because they would at least get an answer without getting yelled at.

Initially this sounds great. But it also means that you want to extract knowledge from a community, while mechanically eliding any values or norms that the community may want to impart as part of offering that knowledge. As someone who spent many years in a community tech support role, this is worrying. Many requests for support are people asking how to do things that will momentarily solve a superficial problem but create a long-term reliability problem or even an immediate security risk, that the question-asker doesn't want to hear about. Consider the question "I'm tired of entering my password so much, how do I make it so my laptop unlocks automatically". An obsequious chatbot will helpfully tell you how to do this without pushback.

But, this is also a sort of ethically murky area. The Linux community is somewhat famously, for many years now, a toxic cesspool of general hostility, misogyny, etc. It is certainly a good thing that people can get access to this knowledge without subjecting themselves to abuse. But it also means that the people with the power and the privilege to change the community for the better can just quietly withdraw, rather than fixing the problems. It also means that the positive elements of culture cannot be transmitted, and people will have no opportunity to learn about unknown unknowns.

In this case, the "adversarial" communication is with society. The thing that using an LLM for search lets you do is withdraw from society and avoid forming any personal connections. There are some personal connections which are painful and annoying, and so that can feel like a momentary balm. But the need to make connections in general is, like, the concept of society itself.

Who Am I Hurting?

LLMs are good at adversarial communication. They are so good at it, relative to their other benefits, that they will tend to make communications adversarial if you are not remaining vigilant about the possibility that it might do so. My request to you, dear reader, if you are going to use such tools, is to always ask yourself, "who might I be hurting, if I use an LLM for this?"

If you're using an "AI", who is its adversary? If you haven't given it one yet, who might the "AI" turn into an adversary? Who might you overwhelm with an asymmetric amount of output, or, if you're receiving information and not sending it, who are you taking that information from without consulting?

Figure out the answers to these questions and conduct yourself accordingly; the answer might be "yourself".

Acknowledgments

Thank you to my patrons who are supporting my writing on this blog. If you like what you've read here and you'd like to read more of it, or you'd like to support my various open-source endeavors, you can support my work as a sponsor!

23 Jun 2026 8:06pm GMT

Codecov's unreliability breaking CI on my open source projects has been a constant source of frustration for me for years. I have found a way to enforce coverage over a whole GitHub Actions build matrix that doesn't rely on third-party services.

09 Jun 2026 12:00am GMT

Let's say you're writing a Python library.

In this library, you have some collection of state that represents "options" or "configuration" for a bunch of operations. Such a set of options is a bundle of potentially ever-increasing complexity. Thus, you will want it to have an extremely minimal compatibility surface, with a very carefully chosen public interface, that is either small, or perhaps nothing at all. Such an object conveys state and might have some private behavior, but all you want consumers to be able to do is build it in very constrained, specific ways, and then pass it along as a parameter to your own APIs.

By way of example, imagine that you're wrapping a library that handles shipping physical packages.

There are a zillion ways to do it ship a package. There are different carriers who can ship it for you. There's air freight, and ground freight, and sea freight. There's overnight shipping. There's the option to require a signature. There's package tracking and certified mail. Suffice it to say, lots of stuff.

If you are starting out to implement such a library, you might need an object called something like ShippingOptions that encapsulates some of this. At the core of your library you might have a function like this:

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async def shipPackage(
        how: ShippingOptions,
        where: Address,
    ) -> ShippingStatus:
    ...

If you are starting out implementing such a library, you know that you're going to get the initial implementation of ShippingOptions wrong; or, at the very least, if not "wrong", then "incomplete". You should not want to commit to an expansive public API with a ton of different attributes until you really understand the problem domain pretty well.

Yet, ShippingOptions is absolutely vital to the rest of your library. You'll need to construct it and pass it to various methods like estimateShippingCost and shipPackage. So you're not going to want a ton of complexity and churn as you evolve it to be more complex.

Worse yet, this object has to hold a ton of state. It's got attributes, maybe even quite complex internal attributes that relate to different shipping services.

Right now, today, you need to add something so you can have "no rush", "standard" and "expedited" options. You can't just put off implementing that indefinitely until you can come up with the perfect shape. What to do?

The tool you want here is the opaque data type design pattern. C is lousy with such things (FILE, pthread_*_t, fd_set, etc). A typedef in a header file can easily achieve this.

But in Python, if you expose a dataclass - or any class, really - even if you keep all your fields private, the constructor is still, inherently, public. You can make it raise an exception or something, but your type checker still won't help your users; it'll still look like it's a normal class.

Luckily, Python typing provides a tool for this: typing.NewType.

Let's review our requirements:

1. We need a type that our client code can use in its type annotations; it needs to be public.
2. They need to be able to consruct it somehow, even if they shouldn't be able to see its attributes or its internal constructor arguments.
3. To express high-level things (like "ship fast") that should stay supported as we add more nuanced and complex configurations in the future (like "ship with the fastest possible option provided by the lowest-cost carrier that supports signature verification").

In order to solve these problems respectively, we will use:

1. a public NewType, which gives us our public name...
2. which wraps a private class with entirely private attributes, to give us an actual data structure, while not exposing the constructor,
3. a set of public constructor functions, which returns our NewType.

When we put that all together, it looks like this:

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from dataclasses import dataclass
from typing import Literal, NewType

@dataclass
class _RealShipOpts:
    _speed: Literal["fast", "normal", "slow"]

ShippingOptions = NewType("ShippingOptions", _RealShipOpts)

def shipFast() -> ShippingOptions:
    return ShippingOptions(_RealShipOpts("fast"))

def shipNormal() -> ShippingOptions:
    return ShippingOptions(_RealShipOpts("normal"))

def shipSlow() -> ShippingOptions:
    return ShippingOptions(_RealShipOpts("slow"))

As a snapshot in time, this is not all that interesting; we could have just exposed _RealShipOpts as a public class and saved ourselves some time. The fact that this exposes a constructor that takes a string is not a big deal for the present moment. For an initial quick and dirty implementation, we can just do checks like if options._speed == "fast" in our shipping and estimation code.

However, the main thing we are doing here is preserving our flexibility to evolve the related APIs into the future, so let's see how we might do that. For example, let's allow the shipping options to contain a concrete and specific carrier and freight method:

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from dataclasses import dataclass
from enum import Enum, auto
from typing import NewType

class Carrier(Enum):
    FedEx = auto()
    USPS = auto()
    DHL = auto()
    UPS = auto()

class Conveyance(Enum):
    air = auto()
    truck = auto()
    train = auto()

@dataclass
class _RealShipOpts:
    _carrier: Carrier
    _freight: Conveyance

ShippingOptions = NewType("ShippingOptions", _RealShipOpts)

def shipFast() -> ShippingOptions:
    return ShippingOptions(_RealShipOpts(Carrier.FedEx, Conveyance.air))

def shipNormal() -> ShippingOptions:
    return ShippingOptions(_RealShipOpts(Carrier.UPS, Conveyance.truck))

def shipSlow() -> ShippingOptions:
    return ShippingOptions(_RealShipOpts(Carrier.USPS, Conveyance.train))

def shippingDetailed(
    carrier: Carrier, conveyance: Conveyance
) -> ShippingOptions:
    return ShippingOptions(_RealShipOpts(carrier, conveyance))

As a NewType, our public ShippingOptions type doesn't have a constructor. Since _RealShipOpts is private, and all its attributes are private, we can completely remove the old versions.

Anything within our shipping library can still access the private variables on ShippingOptions; as a NewType, it's the same type as its base at runtime, so it presents minimal¹ overhead.

Clients outside our shipping library can still call all of our public constructors: shipFast, shipNormal, and shipSlow all still work with the same (as far as calling code knows) signature and behavior.

If you need to build and convey some state within your public API, while avoiding breakages associated with compatibility churn, hopefully this technique can help you do that!

Acknowledgments

Thanks for reading, and thank you to my patrons who are supporting my writing on this blog. If you like what you've read here and you'd like to read more of it, or you'd like to support my various open-source endeavors, you can support my work as a sponsor.

22 May 2026 12:33am GMT