在 PyQt 中使用 matplotlib 的段错误

问题描述

谁能暗示为什么下面的代码(取自 此处)退出时出现段错误?

Can anyone hint at why the following code (taken from here) segfaults on exit?

"""
This demo demonstrates how to embed a matplotlib (mpl) plot
into a PyQt4 GUI application, including:

* Using the navigation toolbar
* Adding data to the plot
* Dynamically modifying the plot's properties
* Processing mpl events
* Saving the plot to a file from a menu

The main goal is to serve as a basis for developing rich PyQt GUI
applications featuring mpl plots (using the mpl OO API).

Eli Bendersky ([email protected])
License: this code is in the public domain
Last modified: 19.01.2009
"""
import sys, os, random
from PyQt4.QtCore import *
from PyQt4.QtGui import *

import matplotlib
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt4agg import NavigationToolbar2QTAgg as NavigationToolbar
from matplotlib.figure import Figure


class AppForm(QMainWindow):
    def __init__(self, parent=None):
        QMainWindow.__init__(self, parent)
        self.setWindowTitle('Demo: PyQt with matplotlib')

        self.create_menu()
        self.create_main_frame()
        self.create_status_bar()

        self.textbox.setText('1 2 3 4')
        self.on_draw()

    def save_plot(self):
        file_choices = "PNG (*.png)|*.png"

        path = unicode(QFileDialog.getSaveFileName(self,
                        'Save file', '',
                        file_choices))
        if path:
            self.canvas.print_figure(path, dpi=self.dpi)
            self.statusBar().showMessage('Saved to %s' % path, 2000)

    def on_about(self):
        msg = """ A demo of using PyQt with matplotlib:

         * Use the matplotlib navigation bar
         * Add values to the text box and press Enter (or click "Draw")
         * Show or hide the grid
         * Drag the slider to modify the width of the bars
         * Save the plot to a file using the File menu
         * Click on a bar to receive an informative message
        """
        QMessageBox.about(self, "About the demo", msg.strip())

    def on_pick(self, event):
        # The event received here is of the type
        # matplotlib.backend_bases.PickEvent
        #
        # It carries lots of information, of which we're using
        # only a small amount here.
        #
        box_points = event.artist.get_bbox().get_points()
        msg = "You've clicked on a bar with coords:\n %s" % box_points

        QMessageBox.information(self, "Click!", msg)

    def on_draw(self):
        """ Redraws the figure
        """
        str = unicode(self.textbox.text())
        self.data = map(int, str.split())

        x = range(len(self.data))

        # clear the axes and redraw the plot anew
        #
        self.axes.clear()
        self.axes.grid(self.grid_cb.isChecked())

        self.axes.bar(
            left=x,
            height=self.data,
            width=self.slider.value() / 100.0,
            align='center',
            alpha=0.44,
            picker=5)

        self.canvas.draw()

    def create_main_frame(self):
        self.main_frame = QWidget()

        # Create the mpl Figure and FigCanvas objects.
        # 5x4 inches, 100 dots-per-inch
        #
        self.dpi = 100
        self.fig = Figure((5.0, 4.0), dpi=self.dpi)
        self.canvas = FigureCanvas(self.fig)
        self.canvas.setParent(self.main_frame)

        # Since we have only one plot, we can use add_axes
        # instead of add_subplot, but then the subplot
        # configuration tool in the navigation toolbar wouldn't
        # work.
        #
        self.axes = self.fig.add_subplot(111)

        # Bind the 'pick' event for clicking on one of the bars
        #
        self.canvas.mpl_connect('pick_event', self.on_pick)

        # Create the navigation toolbar, tied to the canvas
        #
        self.mpl_toolbar = NavigationToolbar(self.canvas, self.main_frame)

        # Other GUI controls
        #
        self.textbox = QLineEdit()
        self.textbox.setMinimumWidth(200)
        self.connect(self.textbox, SIGNAL('editingFinished ()'), self.on_draw)

        self.draw_button = QPushButton("&Draw")
        self.connect(self.draw_button, SIGNAL('clicked()'), self.on_draw)

        self.grid_cb = QCheckBox("Show &Grid")
        self.grid_cb.setChecked(False)
        self.connect(self.grid_cb, SIGNAL('stateChanged(int)'), self.on_draw)

        slider_label = QLabel('Bar width (%):')
        self.slider = QSlider(Qt.Horizontal)
        self.slider.setRange(1, 100)
        self.slider.setValue(20)
        self.slider.setTracking(True)
        self.slider.setTickPosition(QSlider.TicksBothSides)
        self.connect(self.slider, SIGNAL('valueChanged(int)'), self.on_draw)

        #
        # Layout with box sizers
        #
        hbox = QHBoxLayout()

        for w in [  self.textbox, self.draw_button, self.grid_cb,
                    slider_label, self.slider]:
            hbox.addWidget(w)
            hbox.setAlignment(w, Qt.AlignVCenter)

        vbox = QVBoxLayout()
        vbox.addWidget(self.canvas)
        vbox.addWidget(self.mpl_toolbar)
        vbox.addLayout(hbox)

        self.main_frame.setLayout(vbox)
        self.setCentralWidget(self.main_frame)

    def create_status_bar(self):
        self.status_text = QLabel("This is a demo")
        self.statusBar().addWidget(self.status_text, 1)

    def create_menu(self):
        self.file_menu = self.menuBar().addMenu("&File")

        load_file_action = self.create_action("&Save plot",
            shortcut="Ctrl+S", slot=self.save_plot,
            tip="Save the plot")
        quit_action = self.create_action("&Quit", slot=self.close,
            shortcut="Ctrl+Q", tip="Close the application")

        self.add_actions(self.file_menu,
            (load_file_action, None, quit_action))

        self.help_menu = self.menuBar().addMenu("&Help")
        about_action = self.create_action("&About",
            shortcut='F1', slot=self.on_about,
            tip='About the demo')

        self.add_actions(self.help_menu, (about_action,))

    def add_actions(self, target, actions):
        for action in actions:
            if action is None:
                target.addSeparator()
            else:
                target.addAction(action)

    def create_action(  self, text, slot=None, shortcut=None,
                        icon=None, tip=None, checkable=False,
                        signal="triggered()"):
        action = QAction(text, self)
        if icon is not None:
            action.setIcon(QIcon(":/%s.png" % icon))
        if shortcut is not None:
            action.setShortcut(shortcut)
        if tip is not None:
            action.setToolTip(tip)
            action.setStatusTip(tip)
        if slot is not None:
            self.connect(action, SIGNAL(signal), slot)
        if checkable:
            action.setCheckable(True)
        return action


if __name__ == "__main__":
    app = QApplication(sys.argv)
    form = AppForm()
    form.show()
    app.exec_()

除了退出时出现段错误外，其他方面都正常.

Aside from the segfault on exiting, it works fine otherwise.

版本信息:

misha@misha-desktop:~/co/python/resampling$ python
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import matplotlib
>>> matplotlib.__version__
'0.99.1.1'
misha@misha-desktop:~/co/python/resampling$ qmake-qt4 -v
QMake version 2.01a
Using Qt version 4.6.2 in /usr/lib
misha@misha-desktop:~/co/python/resampling$ pyuic4 --version
Python User Interface Compiler 4.7.2 for Qt version 4.6.2

推荐答案

QApplication 对象在退出期间在 Form 之前被垃圾回收.对您的代码进行更改:

The QApplication object is being garbage collected before the Form during exit. Make this change to your code:

if __name__ == "__main__":
    app = QApplication(sys.argv)
    form = AppForm()
    form.show()
    app.exec_()
    del form

，段错误消失.在PyQt或matplotlib中出现的内容取决于在退出时释放资源时仍然存在的QApplication对象.

and the segfault goes away. It appears something in PyQt or matplotlib depends on the QApplication object still existing when resources are being released on exit.

这篇关于在 PyQt 中使用 matplotlib 的段错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！