A single py2/py3-compatible development image

[Jack Hale]

Work in progress under jackhale/slimmer-dev-env. We need to seperate dev-envs, dev-env-dbg with debugging symbols enabled, and dev-env without. stable will then build off of dev-env-dbg. python3 adds another level of complexity.

[Prof Garth Wells]

The 'real' fix is probably sorting out the Python shebangs so a user can pick their Python version on systems with both Py2 and Py3.

Or we drop support for Py2 . . . .

[Jack Hale]

I think your 'real fix' is the one we should aim for, a dev-env and dev-env-dbg that supports both Python 2 and Python 3.

Dropping Py2 is going to be controversial... I think though with the new @ notation for matrix multiplication, we do now have a killer feature in Py3 for numerical Python users that could persuade a switch. But that is for discussion again on fenics-dev.

[Martin Sandve Alnæs]

Py3 is much slower, all the py3 buildbots take signifiantly longer to run the tests for python dominated work.

[Martin Sandve Alnæs]

Would it work to use a #!/usr/bin/env fenics-python and place a symlink in the path of the currently active fenics environment from fenics-python to the right python version?

[Prof Garth Wells]

@martinal That would be much better than having two dev base images.

[Jack Hale]

Updated title to reflect contents of discussion below better. Now, this issue will track trying to get a single python2/python3 development image running.

[Jack Hale]

Issue #2 was marked as a duplicate of this issue.

[Jack Hale]

Largely resolved, now works on master branches of source code:

fenics-build
rm -rf $HOME/local/src/dolfin/build
FENICS_PYTHON=python3 fenics-build

This could be slicker if DOLFIN built its Python modules separately from the C++ library.