Python's poetry dependency manager allows specifying optional dependencies via command:
$ poetry add --optional redis
Which results in this configuration:
[tool.poetry.dependencies]
python = "^3.8"
redis = {version="^3.4.1", optional=true}
However how do you actually install them? Docs seem to hint to:
$ poetry install -E redis
but that just throws and error:
Installing dependencies from lock file
[ValueError]
Extra [redis] is not specified.
You need to add a tool.poetry.extras group to your pyproject.toml if you want to use the -E flag during install, as described in this section of the docs:
[tool.poetry.extras]
caching = ["redis"]
The key refers to the word that you use with poetry install -E, and the value is a list of packages that were marked as --optional when they were added. There currently is no support for making optional packages part of a specific group during their addition, so you have to maintain this section in your pyproject.toml file by hand.
The reason behind this additional layer of abstraction is that extra-installs usually refer to some optional functionality (in this case caching) that is enabled through the installation of one or more dependencies (in this case just redis). poetry simply mimics setuptools' definition of extra-installs here, which might explain why it's so sparingly documented.