I learned from Debugging a pyQT4 app? how to be able to avoid the
QCoreApplication::exec: The event loop is already running
when running a PyQt5 application and using breakpoints. This works fine for doing prints to the console, but I still have trouble if I want to run matplotlib plt.show() during that breakpoint. Then I get the message above and just an empty figure.
Any idea how to overcome that?
Solved: replace plt.show() with plt.pause(0.01). Thank you @jared.
Below is a full example code. The breakpoint is triggered by pushing the button and I have commented under the breakpoint what I am typing on the console to get the empty figure.
import sys
from PyQt5 import QtWidgets
from PyQt5.QtWidgets import (
QMainWindow, QWidget, QHBoxLayout, QPushButton, QLabel
)
class MainWindow(QMainWindow):
"""Class main window."""
def __init__(self):
super().__init__()
self.setWindowTitle('test')
self.widget = QWidget()
box = QHBoxLayout()
self.widget.setLayout(box)
self.lbl = QLabel('Hello')
box.addWidget(self.lbl)
self.btn = QPushButton('Push to breakpoint')
box.addWidget(self.btn)
self.btn.clicked.connect(self.run_script1)
self.setCentralWidget(self.widget)
def run_script1(self):
breakpoint()
#import matplotlib.pyplot as plt
#plt.plot([1,2,3])
#plt.show() / should be: plt.pause(0.01)
def exit_app(self):
"""Exit app by menu."""
sys.exit()
def prepare_debug():
"""Set a tracepoint in PDB that works with Qt."""
# https://stackoverflow.com/questions/1736015/debugging-a-pyqt4-app
from PyQt5.QtCore import pyqtRemoveInputHook
import pdb
pyqtRemoveInputHook()
# set up the debugger
debugger = pdb.Pdb()
debugger.reset()
# custom next to get outside of function scope
debugger.do_next(None) # run the next command
users_frame = sys._getframe().f_back # frame where user invoked `pyqt_set_trace()`
debugger.interaction(users_frame, None)
if __name__ == '__main__':
prepare_debug()
app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
w.show()
app.exec()
