SolverProblemError with papermill

Information

• 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: Ubuntu 18 LTS

• Poetry version: 1.0.10 (and 1.0.5, too)

• Link of a Gist with the contents of your pyproject.toml file: Not required

Issue

When installing papermill with poetry i got the following error message:

[SolverProblemError]
Because no versions of papermill match >2.1.2,<3.0.0
 and papermill (2.1.2) depends on black (*), papermill (>=2.1.2,<3.0.0) requires black (*).
So, because no versions of black match *
 and **myframework** on papermill (^2.1.2), version solving failed.

It looks like it failed to find any version of black, which is weird.

workaround

I just installed black by hand and papermill after that with:

poetry add black
poetry add papermill

This resolved my issue but I leave it here for the poetry devs and other users running into this issue

[abn]

The root cause here is that when provided black (*) as a dependency; since black only has pre-release versions, no version was detected when resolving for dependencies of paparmill. I have attempted to fix it by modifying currrent behaviour such that such packages fallback to returning pre-release versions if constraint is (*). Alternative fix might be in poetry-core where a dependency that uses an any constraint is enabled to allow pre-release. The latter might have undesired side-effects.

[abn]

Thanks for that. I can reproduce the issue now using:

poetry add --dry-run papermill

I was installing black before papermill; missed the part you said about it being the workaround 😃