Add PySide2 support

[me21]

This is a combination of PRs #87, #88 and #97. I've taken care of reported merge conflicts.

[me21]

Er, the errors on AppVeyor seem nothing to do with the changes.

• PySide on Python 3.4 just returned non-zero exit code, even though the tests have passed.
• PyQt4/5 on Python 3.4 failed to install the prerequisites (perhaps some temporary connection problems with PyPI repository?)
• PyQt5 on Python 3.5 complained about PATH in the log, so I suspect it couldn't find some executables or libraries.

I've noticed two syntax errors in Linux builds which caused PySide and PySide2 to be skipped from testing, I'll fix these and rerun all the tests, though.

[me21]

Okay, PATH errors seem to be harmless since they happen in succesful builds too.
Anyway, these build errors in some of the environments look like they aren't caused by the source code.
For example, import errors in PyQt5 and Python 3.5 are caused by known incompatibility between PyQt5.11 and Python <= 3.5.3: https://riverbankcomputing.com/pipermail/pyqt/2018-July/040514.html

And AppVeyor has exactly Python 3.5.3. When it upgrades to Python 3.5.4, the problem should go away.

[me21]

Another incompatibility is that PySide2 requires Qt 5.11 to be built on Linux, and .travis.yml currently installs Qt 5.9. This needs to be fixed. @harvimt?

[ctismer]

What should that be? QtGui.QApplication is for sure not in PySide2.

[me21]

Yes, QApplication is in QtWidgets there, not in QtGui. It is taken care of in that commit.
I'm afraid I don't fully understand your question. Can you please give me more details on what needs to be done?

[henry232323]

Is this going to be implemented any time soon?

[ghost]

so pyside2 dead for quamash?, @harvimt will there be updates or what else to use pyside2 + qt5 on python3? also: #100

[harvimt]

the test-2019 branch mostly works, but hasn't been tested thoroughly.

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On Sun, Sep 22, 2019 at 4:07 AM hivemall ***@***.***> wrote: so pyside2 dead for quamash, @harvimt <https://github.com/harvimt> will there be updates or what else to use pyside2 + qt5 on python3? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#99?email_source=notifications&email_token=AAA5CQUTPJXQGE4JD2WON7DQK5GW3A5CNFSM4FVIL4A2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD7JD4YQ#issuecomment-533872226>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAA5CQV2BHF64KEPPICB3S3QK5GW3ANCNFSM4FVIL4AQ> .