Debugger is flooded with QObject warnings if ipython is started with gui=qt5/4

Dear ipython team,

I am facing a weird issue and can’t find anything elsewhere.

When I start ipython with any qt backend via ipython3 --gui=qt5 and want to use the debugger, it is flooded with warnings which can only be stopped by exiting the debugger.

In [1]: abc        # trigger error                                                                                                                                                                            
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-1-03cfd743661f> in <module>
----> 1 abc 

NameError: name 'abc' is not defined

In [2]: %debug        # debug post-mortem                                                                                                                                                                                 
> <ipython-input-1-03cfd743661f>(1)<module>()
----> 1 abc

ipdb> QObject: Cannot create children for a parent that is in a different thread.                                                                                                              
(Parent is QApplication(0x3880d10), parent's thread is QThread(0x2df86f0), current thread is QThread(0x7f5bcc00bbd0)
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QApplication(0x3880d10), parent's thread is QThread(0x2df86f0), current thread is QThread(0x7f5bcc00bbd0)
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QApplication(0x3880d10), parent's thread is QThread(0x2df86f0), current thread is QThread(0x7f5bcc00bbd0)
QObject: Cannot create children for a parent that is in a different thread.
[...]

I see the same behavior when debugging with %debug fun(args).

I don’t develop with pyqt5, I only use it for visualization with matplotlib and pyqtgraph. This behavior prevents me from using the debugger, which is very cumbersome. I would be happy about any advice where start looking into this issue.

---

$ python -c "import IPython; print(IPython.sys_info())"
{'commit_hash': '254663068',
 'commit_source': 'installation',
 'default_encoding': 'UTF-8',
 'ipython_path': '/home/user/.local/lib/python3.6/site-packages/IPython',
 'ipython_version': '8.0.0.dev',
 'os_name': 'posix',
 'platform': 'Linux-5.3.0-53-generic-x86_64-with-Ubuntu-18.04-bionic',
 'sys_executable': '/usr/bin/python3',
 'sys_platform': 'linux',
 'sys_version': '3.6.9 (default, Apr 18 2020, 01:56:04) \n[GCC 8.4.0]'}

[cpbl]

@clemisch Thanks!!

pip3 install --upgrade --user prompt_toolkit

seems to solve the problem for me.

[jdmcbr]

Thanks @clemisch @cpbl @tacaswell for raising the issue and figuring out a solution. I just ran into the same issue after upgrading to ubuntu 20.04. Initially, the prompt_toolkit update did not resolve the issue for me, but I then noticed that I had prompt_toolkit==3.0.6 rather than prompt_toolkit==3.0.5. With 3.0.5, the issue went away. I wanted to document that here since this was the first post I found when I ran into the QObject warnings.