In a virtualenv using Python 3.9.15, a poetry install failed with the
following message:
Updating dependencies Resolving dependencies... The current project's Python requirement (>=3.9,<4.0) is not compatible with some of the required packages Python requirement: - numpy requires Python >=3.7,<3.11, so it will not be satisfied for Python >=3.11,<4.0
As Python 3.9.1 satisfies both the “current project’s Python requirement” and that of numpy, I wondered why the command failed. Some googling lead me to this question in the poetry FAQ:
Unlike pip, Poetry doesn’t resolve for just the Python in the current environment. Instead it makes sure that a dependency is resolvable within the given Python version range in pyproject.toml.
It took me a while to let this sink in but it totally makes sense: you have a project that states “I work with Python >=3.9,<4.0” even though one of its dependencies states “I only work with Python >=3.7,<3.11”. They cannot both be right so Poetry does the right things and aborts.
This brings me to another point: the Python requirement “>=3.9,<4.0” makes sense if Python adheres to semantic versioning. Unfortunately, according to this discussion, it does not:
Despite similarities, Python does not use the popular semantic versioning_ scheme, which was published several decades after Python.
This doesn’t mean Python 3.11 isn’t compatible to a Python 3.9 for a particular code base, but there are no guarantees that it is. So you might want to rethink a Python requirement like “>=3.9,<4.0”.