BPL BPL - 2 months ago 11
Python Question

Why is QColorDialog.getColor crashing unexpectedly?

I got this little mcve code:

import sys
import re

from PyQt5 import QtGui, QtWidgets, QtCore
from PyQt5.Qsci import QsciScintilla
from PyQt5 import Qsci


class SimpleEditor(QsciScintilla):

def __init__(self, language=None, parent=None):
super().__init__(parent)

font = QtGui.QFont()
font.setFamily('Courier')
font.setFixedPitch(True)
font.setPointSize(10)
self.setFont(font)
self.setMarginsFont(font)
fontmetrics = QtGui.QFontMetrics(font)
self.setMarginsFont(font)
self.setMarginWidth(0, fontmetrics.width("00000") + 6)
self.setMarginLineNumbers(0, True)
self.setMarginsBackgroundColor(QtGui.QColor("#cccccc"))
self.setBraceMatching(QsciScintilla.SloppyBraceMatch)
self.setCaretLineVisible(True)
self.setCaretLineBackgroundColor(QtGui.QColor("#E8E8FF"))

if language:
self.lexer = getattr(Qsci, 'QsciLexer' + language)()
self.setLexer(self.lexer)

self.SendScintilla(QsciScintilla.SCI_FOLDALL, True)
self.setAutoCompletionThreshold(1)
self.setAutoCompletionSource(QsciScintilla.AcsAPIs)
self.setFolding(QsciScintilla.BoxedTreeFoldStyle)

# Signals/Slots
self.cursorPositionChanged.connect(self.on_cursor_position_changed)
self.copyAvailable.connect(self.on_copy_available)
self.indicatorClicked.connect(self.on_indicator_clicked)
self.indicatorReleased.connect(self.on_indicator_released)
self.linesChanged.connect(self.on_lines_changed)
self.marginClicked.connect(self.on_margin_clicked)
self.modificationAttempted.connect(self.on_modification_attempted)
self.modificationChanged.connect(self.on_modification_changed)
self.selectionChanged.connect(self.on_selection_changed)
self.textChanged.connect(self.on_text_changed)
self.userListActivated.connect(self.on_user_list_activated)

def on_cursor_position_changed(self, line, index):
text = self.text(line)
for match in re.finditer('(?:^|(?<=\W))\d+(?:\.\d+)?(?=$|\W)', text):
start, end = match.span()
if start <= index <= end:
pos = self.positionFromLineIndex(line, start)
x = self.SendScintilla(
QsciScintilla.SCI_POINTXFROMPOSITION, 0, pos)
y = self.SendScintilla(
QsciScintilla.SCI_POINTYFROMPOSITION, 0, pos)
point = self.mapToGlobal(QtCore.QPoint(x, y))
num = float(match.group())
message = 'number: %s' % num
break
else:
point = QtCore.QPoint(0, 0)
message = ''
QtWidgets.QToolTip.showText(point, message)
color = QtWidgets.QColorDialog.getColor()

def on_copy_available(self, yes):
print('-' * 80)
print("on_copy_available")

def on_indicator_clicked(self, line, index, state):
print("on_indicator_clicked")

def on_indicator_released(self, line, index, state):
print("on_indicator_released")

def on_lines_changed(self):
print("on_lines_changed")

def on_margin_clicked(self, margin, line, state):
print("on_margin_clicked")

def on_modification_attempted(self):
print("on_modification_attempted")

def on_modification_changed(self):
print("on_modification_changed")

def on_selection_changed(self):
print("on_selection_changed")

def on_text_changed(self):
print("on_text_changed")

def on_user_list_activated(self, id, text):
print("on_user_list_activated")


def show_requirements():
print(sys.version)
print(QtCore.QT_VERSION_STR)
print(QtCore.PYQT_VERSION_STR)

if __name__ == "__main__":
show_requirements()

app = QtWidgets.QApplication(sys.argv)

ex = QtWidgets.QWidget()
hlayout = QtWidgets.QHBoxLayout()
ed = SimpleEditor("JavaScript")

hlayout.addWidget(ed)

ed.setText("""#ifdef GL_ES
precision mediump float;
#endif

#extension GL_OES_standard_derivatives : enable

uniform float time;
uniform vec2 mouse;
uniform vec2 resolution;

void main( void ) {

vec2 st = ( gl_FragCoord.xy / resolution.xy );
vec2 lefbot = step(vec2(0.1), st);
float pct = lefbot.x*lefbot.y;
vec2 rigtop = step(vec2(0.1), 1.-st);
pct *= rigtop.x*rigtop.y;
vec3 color = vec3(pct);

gl_FragColor = vec4( color, 1.0 );""")

ex.setLayout(hlayout)
ex.show()
ex.resize(800, 600)

sys.exit(app.exec_())


For some unknown reason, when I press OK after picking up a color the script will crash unexpectedly, here's a video showing what I mean.

Any idea why this would happen?

Answer

Opening a dialog with a blocking exec() inside the cursor-change handler seems like a bad idea, so I'm not surprised it crashes. It will be much safer to open the dialog asynchronously and use a signal/slot to handle the result. Using a closure with open() would seem best, as it will give access to the current local variables:

class SimpleEditor(QsciScintilla):
    def __init__(self, language=None, parent=None):
        super().__init__(parent)
        ...
        self.colors = QtWidgets.QColorDialog(self)
        self.colors.setModal(True)

    def on_cursor_position_changed(self, line, index):
        text = self.text(line)
        for match in re.finditer('(?:^|(?<=\W))\d+(?:\.\d+)?(?=$|\W)', text):
            start, end = match.span()
            if start <= index <= end:
                pos = self.positionFromLineIndex(line, start)
                x = self.SendScintilla(
                    QsciScintilla.SCI_POINTXFROMPOSITION, 0, pos)
                y = self.SendScintilla(
                    QsciScintilla.SCI_POINTYFROMPOSITION, 0, pos)
                point = self.mapToGlobal(QtCore.QPoint(x, y))
                num = float(match.group())
                message = 'number: %s' % num

                def handler():
                    print(message)
                    print(self.colors.selectedColor().name())

                self.colors.open(handler)

                break