Poetry does not handle full Python version markers correctly

[cjolowicz]

Poetry does not install dependencies into an environment if the dependency has a marker with a full three-digit Python version, even though the environment matches the marker.

For example, the pyproject.toml below is for a project requiring Python 3.6.1 and higher. It also uses the backport of dataclasses to Python 3.6.

(This is not an uncommon situation. Packages like pre-commit explicitly exclude 3.6.0 due to a broken NamedTuple implementation. If such packages are added as dependency, our package also needs to exclude it.)

[tool.poetry]
name = "example"
version = "0.1.0"
description = ""
authors = ["user <[email protected]>"]

[tool.poetry.dependencies]
python = "^3.6.1"
dataclasses = {version = "^0.7", python = ">= 3.6.1, < 3.7"}

[tool.poetry.dev-dependencies]

[build-system]
requires = ["poetry>=0.12"]
build-backend = "poetry.masonry.api"

If we create an environment with the latest Python 3.6, dataclasses is not installed:

$ poetry env use 3.6
Creating virtualenv example-TsH6FKJq-py3.6 in ~/Library/Caches/pypoetry/virtualenvs
Using virtualenv: ~/Library/Caches/pypoetry/virtualenvs/example-TsH6FKJq-py3.6

$ poetry run python -V
Python 3.6.10

$ poetry run pip freeze | grep dataclasses

$ poetry export --format=requirements.txt | grep dataclasses
dataclasses==0.7; python_version >= "3.6.1" and python_version < "3.7" \

Note that the generated requirements.txt is invalid. The python_version marker cannot contain the full three-digit version. Instead python_full_version should be used. See PEP 508.

[RauliRuohonen]

[...] if the dependency has a marker with a full three-digit Python version [...]

The python_version marker cannot contain the full three-digit version. Instead python_full_version should be used.

This focuses on three-digit versions, but the requirements.txt issue at least can occur with two-digit versions as well:

pyenv local 3.6.1
poetry new foo
cd foo
perl -pe 's/python = "\^3.6"/python = "~3.6.1"/' -i pyproject.toml
poetry add fsspec==0.8.4
poetry export -f requirements.txt -o requirements.txt
pip install -r requirements.txt

says

Ignoring fsspec: markers 'python_version > "3.6"' don't match your environment

This is wrong, even though the requirement python_version > "3.6" has only a two-digit version number in it. The reason is the strict comparison: it basically says "the next version after 3.6 or newer", but "the next version" is different for python_version (3.7) and python_full_version (3.6.1). The latter is what is meant, but not what is said.

The original requirement for fsspec 0.8.4 is Requires-Python: >3.6 in its METADATA file. Although this has two digits, it's basically the same thing as >=3.6.1: if you run pip install fsspec==0.8.4 on Python 3.6.0 it fails, but on 3.6.1 it works. Since >3.6 is basically the same requirement as >=3.6.1, it has the same problem: a python_version constraint cannot express it.

Using python_full_version fixes this, too.

[dimbleby]

results of export today for the two cases described are

dataclasses==0.7 ; python_full_version >= "3.6.1" and python_version < "3.7"

and

fsspec==0.8.4 ; python_full_version >= "3.6.1" and python_full_version < "3.7.0"

which both use python_full_version as desired.

[github-actions]

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