[tool.poetry.dependencies]
python = "~2.7, >=3.4, <3.8"

$ poetry install -vvv

[AttributeError]
EmptyConstraint instance has no attribute 'min'

Traceback (most recent call last):
  File "/Users/me/.poetry/lib/poetry/_vendor/py2.7/clikit/console_application.py", line 131, in run
    status_code = command.handle(parsed_args, io)
  File "/Users/me/.poetry/lib/poetry/_vendor/py2.7/clikit/api/command/command.py", line 120, in handle
    status_code = self._do_handle(args, io)
  File "/Users/me/.poetry/lib/poetry/_vendor/py2.7/clikit/api/command/command.py", line 163, in _do_handle
    self._dispatcher.dispatch(PRE_HANDLE, event)
  File "/Users/me/.poetry/lib/poetry/_vendor/py2.7/clikit/api/event/event_dispatcher.py", line 22, in dispatch
    self._do_dispatch(listeners, event_name, event)
  File "/Users/me/.poetry/lib/poetry/_vendor/py2.7/clikit/api/event/event_dispatcher.py", line 89, in _do_dispatch
    listener(event, event_name, self)
  File "/Users/me/.poetry/lib/poetry/console/config/application_config.py", line 86, in set_env
    poetry = command.poetry
  File "/Users/me/.poetry/lib/poetry/console/commands/command.py", line 10, in poetry
    return self.application.poetry
  File "/Users/me/.poetry/lib/poetry/console/application.py", line 49, in poetry
    self._poetry = Factory().create_poetry(Path.cwd())
  File "/Users/me/.poetry/lib/poetry/factory.py", line 90, in create_poetry
    package.python_versions = constraint
  File "/Users/me/.poetry/lib/poetry/packages/project_package.py", line 45, in python_versions
    create_nested_marker('python_version', self._python_constraint)
  File "/Users/me/.poetry/lib/poetry/packages/utils/utils.py", line 214, in create_nested_marker
    if constraint.min is not None:

$ poetry check
All set!