Debugging a pyQT4 app?

Question

I have a fairly simple app built with pyqt4. I wanted to debug one of the functions connected to one of the buttons in my app. However, when I do the following

python -m pdb app.pyw > break app.pyw:55 # This is where the signal handling function starts.

things don't quite work like I'd hope. Instead of breaking in the function where I've set the breakpoint and letting me step through it, the debugger enters an infinite loop printing out QCoreApplication::exec: The event loop is already running and I am unable to input anything. Is there a better way to do this?

Just to know, what's on line 55? Is where you register the signal or is it the function that handles it? — Federico klez Culloca
– Federico klez Culloca, Commented Nov 15, 2009 at 0:36
I think this is not a fully answer, but you could try ERIC as a GUI-Debugger for Python and PyQt: eric-ide.python-projects.org — Berschi
– Berschi, Commented Nov 15, 2009 at 11:19

Martin Tournoij · Accepted Answer · 2015-06-07 22:01:51Z

You need to call QtCore.pyqtRemoveInputHook. I wrap it in my own version of set_trace:

def debug_trace(): '''Set a tracepoint in the Python debugger that works with Qt''' from PyQt4.QtCore import pyqtRemoveInputHook # Or for Qt5 #from PyQt5.QtCore import pyqtRemoveInputHook from pdb import set_trace pyqtRemoveInputHook() set_trace()

And when you are done debugging, you can call QtCore.pyqtRestoreInputHook(), probably best when you are still in pdb, and then after you hit enter, and the console spam is happening, keep hitting 'c' (for continue) until the app resumes properly. (I had to hit 'c' several times for some reason, it kept going back into pdb, but after hitting it a few times it resumed normally)

For further info Google "pyqtRemoveInputHook pdb". (Really obvious isn't it? ;P)

Useful answer, just for reference I found that this worked with PyQt4, but not with PySide.

Community · Accepted Answer · 2017-05-23 11:46:58Z

I had to use a "next" command at the trace point to get outside of that function first. For that I made a modification of the code from mgrandi:

def pyqt_set_trace(): '''Set a tracepoint in the Python debugger that works with Qt''' from PyQt4.QtCore import pyqtRemoveInputHook import pdb import sys 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 the user invoked `pyqt_set_trace()` debugger.interaction(users_frame, None)

This worked for me. I found the solution from here : Python (pdb) - Queueing up commands to execute

Phillip M. Feldman · Accepted Answer · 2020-03-26 20:56:30Z

In my tests, jamk's solution works, while the previous one, although simpler, does not.

In some situations, for reasons that are unclear to me, I've been able to debug Qt without doing any of this.

Collectives™ on Stack Overflow

Debugging a pyQT4 app?

3 Answers 3

1 Comment

1 Comment

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

Comments

Linked

Related