Require ipykernel<6

[mdickinson]

Envisage doesn't currently work with ipykernel 6.0 and later, and it looks as though substantial effort is required to make it work; see #448.

In the meantime, we should make sure that a pip install envisage[ipython] avoids ipykernel version 6 and later.

[mdickinson]

This should really have a test, in the form of a GitHub Actions workflow that runs the test suite after a pip install .[ipython].

Right now, even after that pip install, IPython-related tests are still skipped, because ipykernel depends on ipython_genutils but doesn't declare that dependence.

[mdickinson]

because ipykernel depends on ipython_genutils but doesn't declare that dependence.

Hmm. The PyPI page for ipython_genutils says I'm supposed to pretend it doesn't exist. That's a bit awkward here.

What seems to be happening:

• ipykernel < 6, >= 4 requires ipython_genutils to function, but doesn't declare that dependence
• ipykernel also requires traitlets
• traitlets < 5.1 requires ipython_genutils, and does declare that dependence
• traitlets >= 5.1 (released two days ago) no longer requires ipython_genutils

The result is that as of right now, if you do a pip install 'ipykernel<6' into a clean venv and then try to import ipykernel, that import fails:

mdickinson@mirzakhani Desktop % python -m venv --clear testing && source testing/bin/activate
(testing) mdickinson@mirzakhani Desktop % pip install 'ipykernel<6'
Collecting ipykernel<6
  Using cached ipykernel-5.5.5-py3-none-any.whl (120 kB)
Collecting ipython>=5.0.0
  Using cached ipython-7.27.0-py3-none-any.whl (787 kB)
Collecting appnope
  Using cached appnope-0.1.2-py2.py3-none-any.whl (4.3 kB)
Collecting traitlets>=4.1.0
  Using cached traitlets-5.1.0-py3-none-any.whl (101 kB)
Collecting jupyter-client
  Using cached jupyter_client-7.0.2-py3-none-any.whl (122 kB)
Collecting tornado>=4.2
  Using cached tornado-6.1-cp39-cp39-macosx_10_9_x86_64.whl (416 kB)
Collecting pexpect>4.3
  Using cached pexpect-4.8.0-py2.py3-none-any.whl (59 kB)
Collecting prompt-toolkit!=3.0.0,!=3.0.1,<3.1.0,>=2.0.0
  Using cached prompt_toolkit-3.0.20-py3-none-any.whl (370 kB)
Collecting pygments
  Using cached Pygments-2.10.0-py3-none-any.whl (1.0 MB)
Collecting pickleshare
  Using cached pickleshare-0.7.5-py2.py3-none-any.whl (6.9 kB)
Collecting backcall
  Using cached backcall-0.2.0-py2.py3-none-any.whl (11 kB)
Collecting matplotlib-inline
  Using cached matplotlib_inline-0.1.2-py3-none-any.whl (8.2 kB)
Requirement already satisfied: setuptools>=18.5 in ./testing/lib/python3.9/site-packages (from ipython>=5.0.0->ipykernel<6) (57.4.0)
Collecting decorator
  Using cached decorator-5.0.9-py3-none-any.whl (8.9 kB)
Collecting jedi>=0.16
  Using cached jedi-0.18.0-py2.py3-none-any.whl (1.4 MB)
Collecting parso<0.9.0,>=0.8.0
  Using cached parso-0.8.2-py2.py3-none-any.whl (94 kB)
Collecting ptyprocess>=0.5
  Using cached ptyprocess-0.7.0-py2.py3-none-any.whl (13 kB)
Collecting wcwidth
  Using cached wcwidth-0.2.5-py2.py3-none-any.whl (30 kB)
Collecting pyzmq>=13
  Using cached pyzmq-22.2.1-cp39-cp39-macosx_10_15_universal2.whl (2.0 MB)
Collecting nest-asyncio>=1.5
  Using cached nest_asyncio-1.5.1-py3-none-any.whl (5.0 kB)
Collecting entrypoints
  Using cached entrypoints-0.3-py2.py3-none-any.whl (11 kB)
Collecting python-dateutil>=2.1
  Using cached python_dateutil-2.8.2-py2.py3-none-any.whl (247 kB)
Collecting jupyter-core>=4.6.0
  Using cached jupyter_core-4.7.1-py3-none-any.whl (82 kB)
Collecting six>=1.5
  Using cached six-1.16.0-py2.py3-none-any.whl (11 kB)
Installing collected packages: wcwidth, traitlets, six, ptyprocess, parso, tornado, pyzmq, python-dateutil, pygments, prompt-toolkit, pickleshare, pexpect, nest-asyncio, matplotlib-inline, jupyter-core, jedi, entrypoints, decorator, backcall, appnope, jupyter-client, ipython, ipykernel
Successfully installed appnope-0.1.2 backcall-0.2.0 decorator-5.0.9 entrypoints-0.3 ipykernel-5.5.5 ipython-7.27.0 jedi-0.18.0 jupyter-client-7.0.2 jupyter-core-4.7.1 matplotlib-inline-0.1.2 nest-asyncio-1.5.1 parso-0.8.2 pexpect-4.8.0 pickleshare-0.7.5 prompt-toolkit-3.0.20 ptyprocess-0.7.0 pygments-2.10.0 python-dateutil-2.8.2 pyzmq-22.2.1 six-1.16.0 tornado-6.1 traitlets-5.1.0 wcwidth-0.2.5
WARNING: You are using pip version 21.2.3; however, version 21.2.4 is available.
You should consider upgrading via the '/Users/mdickinson/Desktop/testing/bin/python -m pip install --upgrade pip' command.
(testing) mdickinson@mirzakhani Desktop % python -c "import ipykernel"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/mdickinson/Desktop/testing/lib/python3.9/site-packages/ipykernel/__init__.py", line 2, in <module>
    from .connect import *
  File "/Users/mdickinson/Desktop/testing/lib/python3.9/site-packages/ipykernel/connect.py", line 13, in <module>
    from ipython_genutils.path import filefind
ModuleNotFoundError: No module named 'ipython_genutils'

Given that we're supposed to pretend that ipython_genutils doesn't exist, it looks as though the right thing to do may be to restrict the version of traitlets we're using to a version that still requires ipython_genutils.

[mdickinson]

I opened an upstream issue for the ipython_genutils problem: ipython/ipykernel#759

[mdickinson]

For cleanliness, I've extracted the new workflow into its own PR: #450.