Change python version to 3.x

arshbot

Mar 7

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According to poetry's docs, the proper way to setup a new project is with poetry new poetry-demo, however this creates a project based on the now deprecated python2.7 by creating the following toml file:

[tool.poetry]
name = "poetry-demo"
version = "0.1.0"
description = ""
authors = ["Harsha Goli <harshagoli@gmail.com>"]

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

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

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

How can I update this to 3.7? Simply changing python = "^2.7" to python = "^3.7" results in the following error when poetry install is run:

[SolverProblemError]
The current project's Python requirement (2.7.17) is not compatible with some of the required packages Python requirement:
  - zipp requires Python >=3.6

Because no versions of pytest match >=4.6,<4.6.9 || >4.6.9,<5.0
 and pytest (4.6.9) depends on importlib-metadata (>=0.12), pytest (>=4.6,<5.0) requires importlib-metadata (>=0.12).
And because no versions of importlib-metadata match >=0.12,<1.5.0 || >1.5.0
 and importlib-metadata (1.5.0) depends on zipp (>=0.5), pytest (>=4.6,<5.0) requires zipp (>=0.5).
Because zipp (3.1.0) requires Python >=3.6
 and no versions of zipp match >=0.5,<3.1.0 || >3.1.0, zipp is forbidden.
Thus, pytest is forbidden.
So, because poetry-demo depends on pytest (^4.6), version solving failed.

1 answer

Accepted answer · original discussion

arshbot

Mar 7

Permalink

Interestingly, poetry is silently failing due to a missing package the tool itself relies on and continues to install a broken venv. Here's how you fix it.

sudo apt install python3-venv
poetry env remove python3
poetry install

I had to remove pytest, and then reinstall with poetry add pytest.

EDIT: I ran into this issue again when upgrading a project from python3.7 to python3.8 - for this instead of installing python3-venv, you'd want to install python3.8-venv instead

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ThomasPermalink

Feb 1

When creating a new project, it looks like Poetry inserts the Python version that Poetry itself is running on. So you should check why poetry new poetry-demo was being run on Python 2 instead of 3.