issues with unicode_literals and pysides.QtCore.Slot

[tacaswell]

If I use PySides as the qt4 backend:

tcaswell@mara:~$ ipython --pylab
Python 2.7.5+ (default, Aug  4 2013, 10:07:17) 
Type "copyright", "credits" or "license" for more information.

IPython 2.0.0-dev -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.
Segmentation fault

git bisect points me to commit f4adec7 as the first bad commit.

It works (that is, does not seg-fault) if pyqt is used instead.

I spent a bit of time trying to track down exactly where it was blowing up and it seems to bad a bad interaction between from __future__ import unicode_literals and the pyside version of @QtCore.Slot().

[tacaswell]

also see https://code.google.com/p/spyderlib/issues/detail?id=1466 -> discussion at -https://code.google.com/p/spyderlib/source/detail?r=d12c3026caee -> https://bugreports.qt-project.org/browse/PYSIDE-100

so it looks like this is long standing but unfixed upstream issue.

[tacaswell]

And it looks like the 'fix' is to convert all of the Qt calls to new style calls.

If we look at the top of backend.qt4_editor/formlayout.py (which just happens to be the first place that @QtCore.Slot() is encountered when importing stuff) if we change it to:

from __future__ import absolute_import, division, print_function, unicode_literals

import six
from six.moves import xrange

# History:
# 1.0.10: added float validator (disable "Ok" and "Apply" button when not valid)
# 1.0.7: added support for "Apply" button
# 1.0.6: code cleaning

__version__ = '1.0.10'
__license__ = __doc__

DEBUG = False

import sys
STDERR = sys.stderr

from matplotlib.colors import is_color_like
from matplotlib.colors import rgb2hex
from matplotlib.colors import colorConverter

from matplotlib.backends.qt4_compat import QtGui, QtCore
if not hasattr(QtGui, 'QFormLayout'):
    raise ImportError("Warning: formlayout requires PyQt4 >v4.3 or PySide")

import datetime

class ColorButton(QtGui.QPushButton):
    """
    Color choosing push button
    """
    # __pyqtSignals__ = ("colorChanged(QColor)",)

    def __init__(self, parent=None):
        QtGui.QPushButton.__init__(self, parent)
        self.setFixedSize(20, 20)
        self.setIconSize(QtCore.QSize(12, 12))
        # self.connect(self, QtCore.SIGNAL("clicked()"), self.choose_color)
        self._color = QtGui.QColor()

    def choose_color(self):
        color = QtGui.QColorDialog.getColor(self._color,self.parentWidget(),'')
        if color.isValid():
            self.set_color(color)

    def get_color(self):
        return self._color

    @QtCore.Slot(QtGui.QColor)
    def set_color(self, color):
        if color != self._color:
            self._color = color
            # self.emit(QtCore.SIGNAL("colorChanged(QColor)"), self._color)
            pixmap = QtGui.QPixmap(self.iconSize())
            pixmap.fill(color)
            self.setIcon(QtGui.QIcon(pixmap))

    color = QtCore.Property(QtGui.QColor, get_color, set_color)

It does not segfault.

[tacaswell]

Sorry for having a conversation with my self, but it doesn't look too bad to (only ~34 lines need to be changed in only two files (backend_qt4.py and formlayout.py). I will take a crack at this tonight.

[mdboom]

Great. The change to not using 2to3 was just merged yesterday, and I'm glad it's already getting its tyres kicked, and thanks for finding a solution.

[mdboom]

@tacaswell: Thanks. Sorry for the speedbump, but I think we're going to prefer not running 2to3 anymore in the long run.