Missing dependency when installing iPython on Python 2.7

Thanks for this project, I encountered the following missing enum dependency when installing iPython on Python 2.7.

Here’s how I reproduced against poetry 0.10.0.

[tool.poetry]
name = "test"
version = "0.10.0"
description = ""
authors = []

[tool.poetry.dependencies]
python = "2.7"
ipython = "=5.6.0"

And once poetry install is done I tried both poetry run ipython and ipython without success.

Traceback (most recent call last):
  File "/home/simon/.virtualenvs/tmp-33607c6fbabd8b9/bin/ipython", line 7, in <module>
    from IPython import start_ipython
  File "/home/simon/.virtualenvs/tmp-33607c6fbabd8b9/local/lib/python2.7/site-packages/IPython/__init__.py", line 48, in <module>
    from .core.application import Application
  File "/home/simon/.virtualenvs/tmp-33607c6fbabd8b9/local/lib/python2.7/site-packages/IPython/core/application.py", line 23, in <module>
    from traitlets.config.application import Application, catch_config_error
  File "/home/simon/.virtualenvs/tmp-33607c6fbabd8b9/local/lib/python2.7/site-packages/traitlets/__init__.py", line 1, in <module>
    from .traitlets import *
  File "/home/simon/.virtualenvs/tmp-33607c6fbabd8b9/local/lib/python2.7/site-packages/traitlets/traitlets.py", line 49, in <module>
    import enum
ImportError: No module named enum

I assume this is caused by traitlets’s usage of extra_requires for Python 2.

https://github.com/ipython/traitlets/blob/ee1a829fafad654601dc851dc1d4ec79da090913/setup.py#L92

[sdispater]

I think I know where the problem is coming from.

traitlets defines enum34 as a dependency twice:

enum34; python_version=="2.7"
enum34; python_version=="3.3"

Currently, poetry assumes that every dependency appear only once so in this case it picks up the last one: enum34; python_version=="3.3"

That’s why enum34 is not installed for Python 2.7.

I am not sure about the best approach here. While I think the proper way to declare the enum34 dependency should be enum34; python_version in "2.7 3.3", poetry should be able to handle this.

[sdispater]

@bertjwregeer I think #164 is the same issue so we can use it to track this