ModuleNotFoundError: No module named 'poetry.core.packages.dependency_group'

• 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: Gentoo GNU/Linux (rolling)
• Poetry version: 1.2.1 (Core 1.2.0)
• Link of a Gist with the contents of your pyproject.toml file: not applicable

Issue

After a fresh install pip install --user poetry, I wanted to start with poetry --help. I get the following error:

$ poetry --help -vvv
Traceback (most recent call last):
  File "/home/seb/.local/lib/python3.10/site-packages/cleo/application.py", line 329, in run
    exit_code = self._run(io)
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/console/application.py", line 183, in _run
    self._load_plugins(io)
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/console/application.py", line 349, in _load_plugins
    manager.load_plugins()
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/plugins/plugin_manager.py", line 38, in load_plugins
    self._load_plugin_entry_point(ep)
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/plugins/plugin_manager.py", line 76, in _load_plugin_entry_point
    plugin = ep.load()  # type: ignore[no-untyped-call]
  File "/usr/lib/python3.10/importlib/metadata/__init__.py", line 171, in load
    module = import_module(match.group('module'))
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/home/seb/.local/lib/python3.10/site-packages/poetry_plugin_export/plugins.py", line 7, in <module>
    from poetry_plugin_export.command import ExportCommand
  File "/home/seb/.local/lib/python3.10/site-packages/poetry_plugin_export/command.py", line 4, in <module>
    from poetry.console.commands.group_command import GroupCommand
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/console/commands/group_command.py", line 6, in <module>
    from poetry.core.packages.dependency_group import MAIN_GROUP
ModuleNotFoundError: No module named 'poetry.core.packages.dependency_group'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/seb/.local/bin/poetry", line 8, in <module>
    sys.exit(main())
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/console/application.py", line 388, in main
    exit_code: int = Application().run()
  File "/home/seb/.local/lib/python3.10/site-packages/cleo/application.py", line 334, in run
    self.render_error(e, io)
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/console/application.py", line 175, in render_error
    self.set_solution_provider_repository(self._get_solution_provider_repository())
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/console/application.py", line 377, in _get_solution_provider_repository
    from poetry.mixology.solutions.providers.python_requirement_solution_provider import (  # noqa: E501
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/mixology/__init__.py", line 5, in <module>
    from poetry.mixology.version_solver import VersionSolver
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/mixology/version_solver.py", line 11, in <module>
    from poetry.mixology.failure import SolveFailure
  File "/home/seb/.local/lib/python3.10/site-packages/poetry/mixology/failure.py", line 6, in <module>
    from poetry.core.semver.helpers import parse_constraint
ModuleNotFoundError: No module named 'poetry.core.semver.helpers'

I actually installed poetry-core via my operating system’s package manager beforehands, which installed poetry-core 1.0.8 in the system, but this should not be a problem, since it was installed into /usr/lib/python3.10/site-packages, which comes after /home/seb/.local/lib/python3.10/site-packages on sys.path. (still, /usr/lib/python3.10 comes before it, if that is of any relevance). The pip install --user poetry did install poetry-core 1.2.0 in my .local folder.

[SebAlbert]

So I’ve essentially found that poetry-core used to be an explicit package in 1.0.8 and has become a namespace package as of 1.1.0. (see https://github.com/python-poetry/poetry-core/commit/fa93845ed48f8ba392da3628fd5718a84ebae5d6 ) Bottom line: One must be aware that Python “namespace packages” can lead to version conflicts that are not fully mitigated by just the order of the import path. A clear explanation (easier to read than official Python docs) is on this StackOverflow answer: https://stackoverflow.com/questions/21819649/namespace-vs-regular-package

If either one of them gain an __init__.py that becomes the package - and you no longer get the unification as the other directory is ignored.

[neersighted]

Keep in mind that user installs are not suggested for exactly this reason – use of a virtual environment will prevent this kind of issue. Thanks for digging in!