poetry and python version errors when upgrading from python 2.7 to 3.7

Question

I have started a learning effort to teach myself python. The project started on my mac with python 2.7 as the installed version. On the advice from a friend, I installed poetry to do dependency handling. This worked extremely well.

Before long though I realized how out of date python 2.7 was and tried to upgrade. I did so through homebrew and that seemed to break a lot. python --versoin still shows 2.7 and although I can call python3 --version and see the correct my project still seems to be stuck on 2.7 even when #!/usr/bin/env python3 is at the top of the files. To make matters worse doing a poetry up won't upgrade my python dependency in the project and changing that value in the pyproject.toml brakes everything. I have a dependency that seems to have broken along the way but can't do anything about it with broken poetry/python version mess. The error is below from the poetry.

So taking this from the top how do I get things to start using the correct version of python?

My bash_profile has

PATH="/Library/Frameworks/Python.framework/Versions/3.7/bin:${PATH}"
export PATH

poetry install

[EnvCommandError]                                                                           
Command ['/Users/username/Library/Caches/pypoetry/virtualenvs/PyGameEngine-py2.7/bin/python', '-'] errored with the following return code -6, and output:           
dyld: Library not loaded: @executable_path/../.Python                                                    
  Referenced from: /Users/username/Library/Caches/pypoetry/virtualenvs/PyGameEngine-py2.7/bin/python  
  Reason: image not found                                                                                
input was : import sys                                                                                   
if hasattr(sys, "real_prefix"):                                                                          
    print(sys.real_prefix)                                                                               
elif hasattr(sys, "base_prefix"):                                                                        
    print(sys.base_prefix)                                                                               
else:                                                                                                    
    print(sys.prefix)

So deleting the `/Users/username/Library/Caches/pypoetry/virtualenvs/PyGameEngine-py2.7/bin/python` folder got me to the next error that seems to be the root of my issues ```[RuntimeError] The current Python version (2.7.10) is not supported by the project (^3.7) Please activate a compatible Python version``` — mando222, Jul 18 '19 at 10:35
Try running `poetry install` while inside the virtual env. Do `poetry shell` to activate it — arshbot, May 06 '20 at 17:05

score 0 · Accepted Answer · answered May 06 '20 at 16:52

Copying my answer from here

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

If you are still having issues ( namely upgrading your packages to be python3 compliant, you may want to take a look at this answer )

You do know, that he asked about Mac not about Ubuntu? – sannaj May 06 '20 at 16:56 — sannaj, May 06 '20 at 16:56

poetry and python version errors when upgrading from python 2.7 to 3.7

1 Answers1