Bound version constraints (upper caps) are starting to show up in the Python ecosystem. This is causing real world problems with libraries following this recommendation, and is likely to continue to get worse; this practice does not scale to large numbers of libraries or large numbers of users. In this discussion I would like to explain why always providing an upper limit causes far more harm than good even for true SemVer libraries, why libraries that pin upper limits require more frequent updates rather than less, and why it is not scalable. After reading this, hopefully you will always consider every cap you add, you will know the (few) places where pinning an upper limit is reasonable, and will possibly even avoid using libraries that pin upper limits needlessly until the author updates them to remove these pins.
Also be warned, I pick on Poetry quite a bit. The rising popularity of Poetry is likely due to the simplicity of having one tool vs. many for packaging, but it happens to also have a special dependency solver, a new upper bound syntax, and a strong recommendation to always limit upper versions - in direct opposition to members of the Python core developer team and PyPA developers. Not all libraries with excessive version capping are Poetry projects (like TensorFlow), but many, many of them are. To be clear, Poetry doesn’t force version pinning on you, but it does push you really, really hard to always version cap, and it’s targeting new Python users that don’t know any better yet than to accept bad recommendations. And these affect the whole ecosystem, including users who do not use poetry, but want to depend on libraries that do! I do really like other aspects of Poetry, and would like to eventually help it build binary packages with Scikit-build (CMake) via a plugin, and I use it on some of my projects happily. If I don’t pick on Poetry enough for you, don’t worry, I have a follow-up post that picks on it in much more detail. Also, check out pdm, which gives many of the benefits of Poetry while following PEP standards.[Read More]