任何人都可以提示为什么以下代码（取自here）会在退出时出现段错误吗？
"""
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 (eliben@gmail.com)
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_()
除了退出时的段错误，否则它可以正常工作。
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
答案 0 :(得分：1)
在退出时，在Form之前对QApplication对象进行了垃圾回收。对代码进行此更改：
if __name__ == "__main__":
app = QApplication(sys.argv)
form = AppForm()
form.show()
app.exec_()
del form
并且段错误消失了。在PyQt或matplotlib中出现的东西依赖于在退出时释放资源时仍然存在的QApplication对象。