dependency resolution bug: kedro range not satisfied despite it actually being satisfied

[amasad]

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Reproducible on macOS 10.13.6 and on Ubuntu 18.04.4 LTS

• Poetry version: reproducible on 0.12.16 and 0.12.17

• Link of a Gist with the contents of your pyproject.toml file: this has the full repro: https://repl.it/@amasad/kedro

Issue

Kedro package 0.16 specifies python version to be in the range >=3.6, <3.9 but when you try to install on a project with Python 3.8 it errors out:

Resolving dependencies...
   1: fact: poetrybug is 0.1.0
   1: derived: poetrybug
   1: fact: poetrybug depends on kedro (^0.16.0)
   1: selecting poetrybug (0.1.0)
   1: derived: kedro (^0.16.0)
PyPI: 1 packages found for kedro >=0.16.0,<0.17.0
PyPI: Getting info for kedro (0.16.0) from PyPI
   1: fact: kedro (0.16.0) requires Python >=3.6, <3.9
   1: derived: not kedro (0.16.0)
   1: fact: no versions of kedro match >0.16.0,<0.17.0
   1: conflict: no versions of kedro match >0.16.0,<0.17.0
   1: ! kedro (>0.16.0,<0.17.0) is partially satisfied by not kedro (0.16.0)
   1: ! which is caused by "kedro (0.16.0) requires Python >=3.6, <3.9"
   1: ! thus: kedro is forbidden
   1: ! kedro (>=0.16.0,<0.17.0) is satisfied by kedro (^0.16.0)
   1: ! which is caused by "poetrybug depends on kedro (^0.16.0)"
   1: ! thus: version solving failed
   1: Version solving took 0.240 seconds.
   1: Tried 1 solutions.

I made a full repro here https://repl.it/@amasad/poetrybug

[finswimmer]

Hello @amasad ,

you are using a very outdated version of poetry. Please update to newest one by running poetry self:update.

With the current release you will see this error message:

Using version ^0.16.1 for kedro

Updating dependencies
Resolving dependencies... (0.6s)

[SolverProblemError]
The current project's Python requirement (^3.8) is not compatible with some of the required packages Python requirement:
  - kedro requires Python >=3.6, <3.9

Because no versions of kedro match >0.16.1,<0.17.0
 and kedro (0.16.1) requires Python >=3.6, <3.9, kedro is forbidden.
So, because poetrybug depends on kedro (^0.16.1), version solving failed.

poetry's version solving is fundamental different to other programs in that way, that it tries to find a major version of a package, that is compatible to all python versions, to which the current project is compatible, and not just the one you are currently using.

So, in your pyproject.tomlyou define a python version ^3.8 which means >=3.8,<4.0. As the error message stated out kedro is only compatible to >=3.6, <3.9. You have to adopt this in your pyproject.toml to be able to install this package.

fin swimmer

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