Poetry 0.12.3 uses Python 2.7.10 despite specifying 3.7.0

• 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: macOS Mojave
• Poetry version: 0.12.3
• Link of a Gist with the contents of your pyproject.toml file:

Issue

No matter what I do, Poetry uses Python 2.7.10.

For instance, I’ve downloaded and specified Python 3.7.0 with pyenv:

$ pyenv install 3.7.0
$ pyenv local 3.7.0

My pyproject.toml specifies:

[tool.poetry.dependencies]
python = "3.7.0"
...

Yet poetry update yields:

[SolverProblemError]
The current supported Python versions are 2.7.10
Because hug (2.4.1) requires Python >=3.4
 and no versions of hug match >2.4.1,<3.0.0, hug is forbidden.
So, because <...> depends on prodigy (1.6.1) which depends on hug (>=2.4.1,<3.0.0), version solving failed.

I’m completely mystified.

Infuriatingly, if I instead specify python = "3.2" Poetry will gladly use Python 3.2…

[bdoms]

I realize this is a closed issue and I’m not suggesting repoening it, as there isn’t a bug (the program works as designed). However, the behavior is still not ideal, and I found this page because I was running into the same issues still today months later. Not being able to specify a Python version is a huge pain on some systems. In some cases you can’t just switch what the active version is.

So I suggest that being able to specify a Python version be a new feature if it isn’t on the roadmap. That behavior already exists with virtualenv with the -p option, so simply creating something in poetry that could forward along an argument to that would go a long way.

Since I found this while doing random web searches for the problem I also wanted to point out a quick hack I used that effectively solved this problem for me in the hopes that it helps out others. Simply add an alias to your .bashrc or similar, like this:

alias poetry="python3 $HOME/.poetry/bin/poetry"

Voila, the poetry command now uses the version of Python you want.

[sjuxax]

For what it’s worth, this should be considered a bug.

The official recommendation is to leave the primary python binary pointing to Python2 indefinitely to allow smooth co-existence of version-naive scripts, see PEP 394. Python 3.x is only supposed to be accessible by python3. If Python 2 is not installed, there should not be a /usr/bin/python.

Some distributions have chosen to break this packaging recommendation and in general it works OK as long as you’re using software from their repos, where they’ve replaced all the shebangs accordingly, but on many systems, including macOS, it can and will break things to link /usr/bin/python to the 3.x interpreter.

While there’s been some discussion around whether the recommendation should be maintained long-term, given that the official recommendation is for /usr/bin/python to always point to the system’s Python 2.x interpreter, Poetry should not assume that /usr/bin/python always represents the “activated interpreter”.