MNT: more minor tweaks to qt_compat.py

[tacaswell]

If we the backend is not a Qt* backend, a version of pyqt has not been
imported and PyQt5 is not installed qt_compat would raise as
ImportError. Now it will gracefully fall back to PyQt4.

attn @jrevans @mfitzp

[jenshnielsen]

I would raise a warning here

[tacaswell]

Ah, the logic has gotten crossed here. You can fall through this code path as the 'right' thing to do if we had to guess about qt4vqt5 above

[jenshnielsen]

Perhaps I misunderstand, but as far as I can see that will only happen if

• You have specified rcParams['backend.qt4'] = PyQt5 which is clearly wrong.
• Tried using the Qt5Agg backend without installing PyQt5
• if if "PyQt4" in sys.modules or "PySide" in sys.modules: fails if which case this will fail any way.

[tacaswell]

You can also get here if your rcparam is tkagg and you do not have qt5
installed (which is how I found this).

The (new) logic above says that if the rcparam is not set to a qt flavor,
it looks to see if qt4 or pyside is imported, then assumes it should be
using qt5.

On Mon, Sep 28, 2015, 04:30 Jens Hedegaard Nielsen notifications@github.com
wrote:

In lib/matplotlib/backends/qt_compat.py
#5153 (comment):

@@ -109,9 +109,18 @@
except:
res = 'QVariant API v2 specification failed. Defaulting to v1.'
verbose.report(cond + res, 'helpful')

• if QT_API == QT_API_PYQT5:

•    try:
  

•        from PyQt5 import QtCore, QtGui, QtWidgets
  

•        _getSaveFileName = QtWidgets.QFileDialog.getSaveFileName
  

•    except ImportError:
  

•        # fell through, tried PyQt5, failed fall back to PyQt4
  

•        QT_API = rcParams['backend.qt4']
  

Perhaps I misunderstand, but as far as I can see that will only happen if

• You have specified rcParams['backend.qt4'] = PyQt5 which is clearly
  wrong.
• Tried using the Qt5Agg backend without installing PyQt5
• if if "PyQt4" in sys.modules or "PySide" in sys.modules: fails if
  which case this will fail any way.

—
Reply to this email directly or view it on GitHub
https://github.com/matplotlib/matplotlib/pull/5153/files#r40527986.

[jenshnielsen]

Ok fair enough

[tacaswell]

I agree this thing is a mess and needs a overhaul, but i want to get it
fixed enough for the next rc

On Mon, Sep 28, 2015, 06:59 Jens Hedegaard Nielsen notifications@github.com
wrote:

In lib/matplotlib/backends/qt_compat.py
#5153 (comment):

@@ -109,9 +109,18 @@
except:
res = 'QVariant API v2 specification failed. Defaulting to v1.'
verbose.report(cond + res, 'helpful')

• if QT_API == QT_API_PYQT5:

•    try:
  

•        from PyQt5 import QtCore, QtGui, QtWidgets
  

•        _getSaveFileName = QtWidgets.QFileDialog.getSaveFileName
  

•    except ImportError:
  

•        # fell through, tried PyQt5, failed fall back to PyQt4
  

•        QT_API = rcParams['backend.qt4']
  

Ok fair enough

—
Reply to this email directly or view it on GitHub
https://github.com/matplotlib/matplotlib/pull/5153/files#r40539934.

[jenshnielsen]

I agree, part of the mess is my fault