Poetry doesn't use the correct version of Python

Question

I've recently installed both Pyenv and Poetry and want to create a new Python 3.8 project. I've set both the global and local versions of python to 3.8.1 using the appropriate Pyenv commands (pyenv global 3.8.1 for example). When I run pyenv version in my terminal the output is 3.8.1. as expected.

Now, the problem is that when I create a new python project with Poetry (poetry new my-project), the generated pyproject.toml file creates a project with python 2.7:

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

[tool.poetry.dependencies]
python = "^2.7"

[tool.poetry.dev-dependencies]
pytest = "^4.6"

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

It seems that Poetry defaults back to the system version of Python. How do I change this so that it uses the version installed with Pyenv?

Edit

I'm using MacOS, which comes bundled with Python 2.7. I think that might be causing some of the issues here. I've reinstalled Python 3.8 again with Pyenv, but when I hit Poetry install I get the following error:

The currently activated Python version 2.7.16 is not supported by the project (^3.8).
Trying to find and use a compatible version.

[NoCompatiblePythonVersionFound]
Poetry was unable to find a compatible version. If you have one, you can explicitly use it via the "env use" command. 

Should I create an environment explicitly for the project using Pyenv or should the project be able to access the correct Python version after running pyenv local 3.8.1.? When I do the latter, nothing changes and I still get the same errors.

Answer 1

pyproject.toml is used to define all the dependencies for your project, including the supported python version.

The line your complaining about is just saying that the versions of python supported by the project is python2.7 or greater, this is independent of what versions of python you've installed with pyenv.

python = "^2.7"

If you want to update the versions of python supported by the project you can edit the file directly and run poetry update.

---

If you want to use multiple versions of python you need to make sure poetry is using the correct dependencies for the version of python you are using. To change the specific version poetry is using you should use poetry env,

• poetry env list show the versions of python poetry can use
• poetry env use <python> switches poetry to use that version.

For instance on my machine poetry has 3 virtual environments installed and is using the one associated with python3.6:

↪ poetry env list
sipy-a9sqc5pb-py3.6 (Activated)
sipy-a9sqc5pb-py3.7
sipy-a9sqc5pb-py3.8

I'm not sure how these virtual environments with interact with the shivs used by pyenv but their docs have a section relating to it

Managing Virtual Environments

There is a pyenv plugin named pyenv-virtualenv which comes with various features to help pyenv users to manage virtual environments created by virtualenv or Anaconda. Because the activate script of those virtual environments are relying on mutating $PATH variable of user's interactive shell, it will intercept pyenv's shim style command execution hooks. We'd recommend to install pyenv-virtualenv as well if you have some plan to play with those virtual environments.