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?

Answer 1

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
  from pdb import set_trace
  pyqtRemoveInputHook()
  set_trace()

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