• 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).

build environment: https://circleci.com/gh/cjw296/playground/9
config: https://github.com/cjw296/playground/blob/48364861386eeda9d2592423503fe1c50b94cf1b/pyproject.toml

Issue

poetry fails to install more-itertools on python 2.7, even though it's a dependency of pytest.
The workaround is to separately specify it:

cjw296/playground@035f8b5

Looks like the pytest guys had some fun with this too, so suspect it might be a nasty
edge case: pytest-dev/pytest#4770