poetry_fix.py - Work around Poetry bugs

This script contains workarounds for Poetry design decisions and bugs:

  1. Poetry doesn’t support either/or dependencies, but this project needs them. Specifically, we want to install either the released, PyPI-published version of the RunestoneComponents and the BookServer, or the development version of these projects which are cloned to the local filesystem. The RunestoneServer pyproject.toml file therefore contains (with all other dependencies removed for clarity):

    bookserver = "^1.0.0"
    runestone = "^6.1.0"
    bookserver = { path = "../BookServer", develop = true }
    runestone = { path = "../RunestoneComponents", develop = true }

    This breaks Poetry, since it looks for BOTH dependencies during dependency resolution. To work around this, rename_pyproject changes this to:

    bookserver = "^1.0.0"
    runestone = "^6.1.0"
    [tool.no-poetry.dev-dependencies]   # <== CHANGED!
    bookserver = { path = "../BookServer", develop = true }
    runestone = { path = "../RunestoneComponents", develop = true }

    …in production mode; it does the opposite (changes [tool.poetry.dev-dependencies] to [tool.no-poetry.dev-dependencies]) in development mode. This hides the modified section from Poetry, so the file now looks like an either/or project.


  • Make this a poetry plugin, so it would auto-update this on any changes to the project’s pyproject.toml. It looks like plugins aren’t supported until v1.2.0, though.


These are listed in the order prescribed by PEP 8.

Standard library

from pathlib import Path

Third-party imports

import click

Local application imports


Workaround for the main pyproject.toml

This function updates the pyproject.toml in the current directory by switching between a section named [tool.poetry.dev-dependencies] when in development mode or [tool.no-poetry.dev-dependencies] when not in development mode. This is because Poetry does not support either/or dependencies: either resolve dependency x in dev mode, or dependency y when not in dev mode. Instead, it takes a both/and approach: during its dependency resolution phase, it resolves ALL dependencies, then installs a subset (such all non-dev dependencies, or dev and non-dev dependencies). Quoting from the manual:

All dependencies must be compatible with each other across groups since they will be resolved regardless of whether they are required for installation or not (see Installing group dependencies).

Think of dependency groups as labels associated with your dependencies: they don’t have any bearings on whether their dependencies will be resolved and installed by default, they are simply a way to organize the dependencies logically.

Therefore, path based dev-dependencies break ‘install –no-dev’ when the directory does not exist. In addition, if a dependency exists both in the [tool.poetry.dependencies] and the same dependency with a path in [tool.poetry.dev-dependencies] sections, this version of Poetry will place the path in the resulting poetry.lock file even when the --no-dev option is passed, causing Poetry to install the dev version or fail if it’s not available.

As a workaround, this function renames the [tool.poetry.dependencies] section, effectively hiding it, for --no-dev option, and un-hides it otherwise. It then deletes poetry.lock if it makes a change, ensuring that poetry will the run poetry update with these changed dependencies.

def rewrite_pyproject(is_dev: bool) -> None:

Determine the current mode by setting has_dev.

    pyproject = Path("pyproject.toml")
    pp_text = pyproject.read_text()
    dev_section = "\n[tool.poetry.dev-dependencies]\n"
    no_dev_section = "\n[tool.no-poetry.dev-dependencies]\n"
    if dev_section in pp_text:
        has_dev = True
    elif no_dev_section in pp_text:
        has_dev = False
            f"Error: there is no [tool.(no-)poetry.dev-dependencies] section in {pyproject.resolve()}."

Update accordingly.

    if is_dev and not has_dev:
        pp_text = pp_text.replace(no_dev_section, dev_section)
    elif not is_dev and has_dev:
        pp_text = pp_text.replace(dev_section, no_dev_section)

No update needed. We’re done.


Ideally, we’d run poetry update here. However, we’re blocked from doing so by circular dependencies:

  1. In a clean install, the command poetry config virtualenvs.in-project true has not executed yet.

  2. Running this command will first check the dependencies in the existing poetry.lock file and report that directories such as ../BookServer don’t exist. (Why does Poetry do this?)

  3. To update poetry.lock, we can run poetry update.

  4. But poetry update will update the wrong venv, since poetry config virtualenvs.in-project true hasn’t run yet.

  5. Go to step 1.

So, just delete the lock file and let Poetry rebuild it; don’t complain if the file’s already been deleted.


CLI interface

    "--no-dev", is_flag=True, help="Prepare for running poetry install/update --no-dev."
def main(no_dev: bool):

This script works around Poetry limitations to provide support of either/or dependencies.

    is_dev = not no_dev

if __name__ == "__main__":