constraint vs requirement. What's the difference? (programming.dev)

submitted 3 weeks ago* (last edited 3 weeks ago) by logging_strict@programming.dev to c/python@programming.dev

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In a requirements-*.in file, at the top of the file, are lines with -c and -r flags followed by a requirements-*.in file. Uses relative paths (ignoring URLs).

Say have docs/requirements-pip-tools.in

-r ../requirements/requirements-prod.in
-c ../requirements/requirements-pins-base.in
-c ../requirements/requirements-pins-cffi.in

...

The intent is compiling this would produce docs/requirements-pip-tool.txt

But there is confusion as to which flag to use. It's non-obvious.

constraint

Subset of requirements features. Intended to restrict package versions. Does not necessarily (might not) install the package!

Does not support:

editable mode (-e)
extras (e.g. coverage[toml])

Personal preference

always organize requirements files in folder(s)
don't prefix requirements files with requirements-, just doing it here
DRY principle applies; split out constraints which are shared.

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[-] spoonbill@programming.dev 4 points 3 weeks ago

Constraints are useful for restricting build dependencies of your dependencies, especially if they follow PEP-518.

[-] logging_strict@programming.dev 1 points 3 weeks ago

Was working under the assumption that everyone considered constraints (-c) to be non-negotiable required feature.

If only have requirements (-r), in a centralized pyproject.toml, then how to tackle multiple specific dependency hell issues without causing a huge amount of interconnected clutter?

[-] spoonbill@programming.dev 2 points 3 weeks ago

Why do you need to have a centralized pyproject.toml?

[-] logging_strict@programming.dev 1 points 3 weeks ago

Within the context of resolving dependency conflicts, poetry decided pyproject.toml is a great place to put requirements.

This is what people know.

pyproject.toml or venv management should otherwise never come into the conversation.

My personal opinion is: venv, pip, pyenv, pip-tools, and tox are sufficient to manage venvs.

venvs are not required to manage requirement files. It's a convenience so dev tools are accessible.

Currently the options are: poetry or uv.

With honorable mention to pip-compile-multi, which locks dependencies.

poetry and uv manage venvs... Why?

[-] spoonbill@programming.dev 1 points 3 weeks ago

I was asking why you need to have a centralized pyproject.toml file, which is apparently why you need constraint files? Most people don't have this workflow, so are not even aware of constraint files, much less see them as a must-have.

[-] logging_strict@programming.dev 1 points 3 weeks ago

I totally agree with you. So not the best champion of the poetry approach. Someone else would need to step forward, even as devils advocate, and champion poetry. Even if tongue in cheek. Anyone?

Normally, there is no connection between constraint files and pyproject.toml

Python appears to be forever stuck with plain text requirement|constraint files. So putting them into pyproject.toml is just adding an extra layer of complexity.

[-] spoonbill@programming.dev 1 points 3 weeks ago

If most people prefer pyproject.toml over requirements.txt, even if it does not support everything you need, isn't it more likely that you will have to change workflow rather than python remaining stuck with requirement.txt?

[-] logging_strict@programming.dev 1 points 3 weeks ago* (last edited 3 weeks ago)

more likely

That almost sounds like you might consider to jump on polymarket, initiate the prediction, put money down on that prediction creating a position, but need a little nudge.

Are you willing to make that bet? The size of the bet reflects how strongly you feel. Are you going to make this interesting?

The other side of that bet would be:

Could become that guy who extends the theory, makes a better way of doing it, and creates and publishes the package and docs.

And the world+dog recognizes the package amongst the other tools in this genre, rather than i conforming to existing tools (uv or poetry or pip-compile-multi).

In your favor, there are three tools. So three people/teams on this planet have presented a solution. Can count that on one hand with fingers to spare!

On the other hand, lets keep in mind, this is a Python specific forum and everyone here are skilled super talented coders and probably full on freak'n geniuses (lifts hand, pinky to closest edge of mouth, everyone looks around at one another and copies, then looks back at you with an errie almost coordinated synchronized eye brow raise). And i oddly posted about this exact topic. Literally anyone and everyone who has commented could be that guy.

scratches head

looks up with one eye to check star positions

rubs chin

occasional alternating strong eye brow movements ...

(with hand on chin) who is this guy, should i call his bluff by taking a position? Whats the likelihood he's secretly a closet poetry user and just some poser?

If you won, could you be sad?

If you lost, not get upset or ego hurt instead be much happier with the published tool over the money?

What are the odds looking like on this particular prediction?

Looking forward to you posting the URL to the prediction on polymarket then promoting the market to maximize your returns. First in and clean house. Rinse wash and repeat with this blowhard wannabe (referring to myself).

[-] spoonbill@programming.dev 1 points 3 weeks ago

Here is another prediction: the volume of that bet would be nowhere near where it needs to be to make the bet interesting.

Disagree? Create the bet yourself and prove me wrong.

[-] logging_strict@programming.dev 1 points 3 weeks ago

Strategy --> deflection

Involve other people, not yourself; reframe the discussion.

So your predictions are worthless cuz you are unwilling to take on any risk.

Coding involves risk and those willing to take on risk. A gambling man you are not!

Can throw shade and FUD around all day long everyday without consequence or care. Cuz u offer nor put any skin in the game.

Just empty words like a secretary giving a language skill assessment.

So if i said, i see ghosts and dragons and can shit rainbows out of my butt, you'd be too weak to call the bluff.

[-] logging_strict@programming.dev 1 points 3 weeks ago* (last edited 3 weeks ago)

To make this interesting, you could have asked for a stipulation that i fund the other side of the bet. Oddly, you didn't insist on that. Once the bet is funded, drop the make it interesting claim, that's what a bet is.

If i were in your shoes

And believed strongly in your predictions i'd do due diligence.

Read thru the persons github acnt. All the code and mercilessly, but fairly, do a public code review of all public packages, documentation, and commit style. What code quality does this person produce? Whats the likelihood this person could be prepared to possibly collaborate with others?

This is normally enough to evaluate someone. I've ripped people apart who've presented themselves as Python coders and were actually base amateurs.

Here is my github acnt. I submit to ur code review. Meaning, during the code review, any concerns you bring up, i have to defend my actions. Whatever public humiliation you have in store for me, cannot complain or retaliate.

Notice there are no code of conduct files in any of the packages. Free your inner troll and be merciless!

https://github.com/msftcangoblowm

While there, if you like a package, star it

Understand the problem

What would it take to create a solution to this issue?

Does the person, with that github history, clearly understand the issue? Enough to come up with a viable solution?

If had doubts, would admit and say, not confident enough in the prediction any bet could possibly go very wrong. Could admit to having serious doubts without shame.

If had confidence in the prediction, having conducted due diligence, would call the bluff and take the guys money

You took the third option, get called out and proven a non-risk taker and someone who doesn't bother doing their own research. But doesn't mind throwing shade at everyone and everything.

[-] eager_eagle@lemmy.world 1 points 3 weeks ago

are you really asking why use 1 tool instead of 5?

venvs and dependency management are such interconnected concepts, I don't even know how you could sustainably handle them separately.

[-] logging_strict@programming.dev 1 points 3 weeks ago* (last edited 3 weeks ago)

UNIX philosophy. One tool that does one thing well

Best to have a damn good reason when breaking this principle (e.g. vendoring) or be funded by Money McBags

requirements files are requirements files, not venvs. They may install into venv, but they are not venvs themselves. The only thing a venv provides that is of interest to ur requirements files are: the relative folder path (e.g. '.venv') and python interpreter path. Nothing more. When using tox, the py version is hardcoded, so only need to provide the relative folder path.

The venv management tools we have are sufficient. the problem is not the venv, it's managing the requirements files.

Your 1 tool suacks just as much as my 5 tools when it comes to managing requirement files. None of them do the job.

[-] eager_eagle@lemmy.world 2 points 3 weeks ago

The Python env has been trying this multiple tools approach for decades and consistently delivering a worse experience than languages that pack most things in one tool.

Rust is a bliss to use, largely thanks to cargo that takes care of build, dependencies, locking, tests, publishing etc. You say do one thing and do it well. In my experience they often do one thing in a mediocre way, while forcing users to understand which and how to combine dozens of possible tools in a development environment that keeps changing. It's messy, slow, error prone, and requires constant developer attention.

[-] logging_strict@programming.dev 1 points 3 weeks ago

Most languages don't support packages containing multiple languages (C/C++, Cython, and Python). So Python situation is much more complex.

distutils

setuptools is complex

pip is complex

requirements files are complex

space aliens wrote pytest (and pluggy)

publishing and dependencies are super centralized, depending on pypi.org way too much.

Comparing Rust vs Python is nonsense. Rust is a stricter compiler on top of C. It has to deal with legacy C libraries. It has it very very easy.

[-] eager_eagle@lemmy.world 1 points 3 weeks ago

and despite those differences, uv is essentially cargo for Python, showing it is possible.

[-] logging_strict@programming.dev 1 points 3 weeks ago

Which begets the question, why inject an additional toolchain into package when not skilled at all in that toolchain. Can't support issues caused by that toolchain.

[-] Michal@programming.dev 2 points 3 weeks ago

Requirements are literally the packages your project requires to run,down to a specific version if you wish.

Constraints specifies what version of a package to install IF the package is required by your requirements, or by transitive requirement (required by packages you require). If package is not required, the constraint is not used.

I tend to use requirements file to list direct dependencies of my project and their versions. Constraints is useful to pin down and transitive dependencies to make sure they're not accidentally upgraded (repeatable builds) . Also if the 3rd party package drops a requirement you don't have to worry that it'll still be installed if it's still on your constraints. It'll simply not be installed.

[-] logging_strict@programming.dev 1 points 3 weeks ago

Great explanation of the most important difference

[-] eager_eagle@lemmy.world 1 points 3 weeks ago

my personal preference is a pyproject.toml over that mess

[-] logging_strict@programming.dev 2 points 3 weeks ago* (last edited 3 weeks ago)

my position is it's not messy enough

Lets start off by admitting what the goal is.

We all want to avoid dependency hell.

Our primary interest is not merely cleaning up the mess of requirements files.

Cleaning up the mess results in some unintended consequences:

noise
complexity
confusion

noise

All the requirements information is in one place. Sounds great until want to tackle and document very specific issues.

Like when Sphinx dropped support for py39, myst-parser restricted the Sphinx upper bound version, fixed it in a commit, but did not create a release.

Or cffi, every single commit just blows our mind. Adding support for things we all want. So want to set a lower bound cffi version.

My point being, these are all specific issues and should be dealt with separately. And when it's no longer relevant, know exactly what to remove. Zero noise.

complexity

When things go horribly wrong, the wrapper gets in the way. So now have to deal with both the wrapper and the issue. So there is both a learning curve, an API interface, and increased required know how.

The simple answer here is, do not do that.

confusion

When a dependency hell issue arises, have to deal with that and find ourselves drawn to poetry or uv documentation. The issue has nothing to do with either. But we are looking towards them to see how others solve it, in the poetry or uv way.

The only know-how that should be needed is whats in the pip docs.

Whats ur suggestion?

Would prefer to deal with dependency hell before it happens. To do this, the requirements files are broken up, so they are easier to deal with.

Centralizing everything into pyproject.toml does the opposite.

Rather than dealing with the issue beforehand, get to deal with it good and hard afterwards.

[-] spoonbill@programming.dev 2 points 3 weeks ago

But pyproject.toml supports neither locking nor constraints.

[-] eager_eagle@lemmy.world 2 points 3 weeks ago

Ah true, I had the wrong idea about this constraints file. What's your use case?

[-] spoonbill@programming.dev 1 points 3 weeks ago

My only use case so far has been fixing broken builds when a package has build-)ldependencies that don't actually work (e.g. a dependency of a dependency breaks stuff). Not super common, but it happens.

[-] logging_strict@programming.dev 1 points 3 weeks ago

That's a loaded question. Would like to avoid answering atm. Would lead to a package release announcement which this post is not; not prepared to right right now.

Instead here is an admittedly unsatisfactory response which i apologize for.

Wish to have the option to, later, take it back and give the straight exact answer which your question deserves.

my use case is your use case and everyone else's use case.

Avoiding dependency hell while keeping things easily manageable. Breaking up complexity into smallest pieces possible. And having a CLI tool to fix what's fixable while reporting on what's not.

My preference is to do this beforehand.