When installing SlicerElastix it says
File “/Users/alex/Applications/Slicer.app/Contents/Extensions-28138/SlicerElastix/lib/Slicer-4.11/qt-scripted-modules/Elastix.py”, line 330
print e
^
SyntaxError: Missing parentheses in call to ‘print’. Did you mean print(e)?
Thanks for reporting this. Slicer core has been upgraded to Python3 but most extensions have not been made Python3 compatible yet.
@jcfr are you going to submit a pull request for SlicerElastix? In general, do you plan to send pull requests for most extensions?
I am very happy for the python3 upgrade 
Now the bundled python can release the GIL and numpy runs in multiprocessing using several cores.
SlicerElastix has been updated to support Python3.
This will happen on “as needed” basis.
Great, thank you!
Do you mean we can ask for your help whenever we want to upgrade an extension to be compatible with Python3?