The specified Python version (3.8) is not supported by the project (^3.7).

• 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 18.04.3 LTS

• Poetry version: Poetry version 1.0.0

• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/jobevers/a3e674e4f316a6c0ea535ac818bf5f61

Issue

I wanted to start using python 3.8 in a project:

» poetry env use -vvv 3.8.0 

[NoCompatiblePythonVersionFound]
The specified Python version (3.8) is not supported by the project (^3.7).
Please choose a compatible version or loosen the python constraint specified in the pyproject.toml file.

Traceback (most recent call last):
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/clikit/console_application.py", line 131, in run
    status_code = command.handle(parsed_args, io)
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/clikit/api/command/command.py", line 120, in handle
    status_code = self._do_handle(args, io)
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/clikit/api/command/command.py", line 171, in _do_handle
    return getattr(handler, handler_method)(args, io, self)
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/cleo/commands/command.py", line 92, in wrap_handle
    return self.handle()
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/poetry/console/commands/env/use.py", line 23, in handle
    env = manager.activate(self.argument('python'), self._io)
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/poetry/utils/env.py", line 259, in activate
    self.create_venv(io, executable=python, force=create)
  File "/home/jobevers/.local/pipx/venvs/poetry/lib/python3.6/site-packages/poetry/utils/env.py", line 520, in create_venv
    self._poetry.package.python_versions, python_minor

[kamyar]

+1 having this issue at the moment with python 3.8.2.

Edit: changing

[tool.poetry.dependencies]
python = "3.8"

to

[tool.poetry.dependencies]
python = "^3.8"

worked.

I guess initially set it too strictly without knowing

[sdispater]

You should use only the minor version with env use:

poetry env use 3.8

Basically, Poetry looks for a python3.8.0 executable which it does not find leading to this error.