Shaperilio/gui msg

[shaperilio]

Addresses the annoying extra messages as detailed in #14006.

Behavior

The intent is to:

• Communicate when the user installs a hook
• Communicate when the user tries to install a different hook and cannot.
• Communicate when the user uninstalls a hook
• Not communicate when the user tries to install the same hook multiple times, with special care for the "latest version" 'qt' hook request.

Take a system with both PyQt5 and pyside6 installed:

(venv) > ipython
Python 3.10.5 (tags/v3.10.5:f377153, Jun  6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)]
Type 'copyright', 'credits' or 'license' for more information
IPython 8.14.0.dev -- An enhanced Interactive Python. Type '?' for help.

In [1]: %gui qt
Installed qt6 event loop hook.

In [2]: %gui qt5
Cannot switch Qt versions for this session; will use qt6.
Installed qt6 event loop hook.

In [3]: %gui qt

In [4]: %gui qt6

In [5]: %gui tk
Shell is already running a gui event loop for qt6. Call with no arguments to disable the current loop.

In [6]: %gui
GUI event loop hook for tk removed.

In [7]: %gui tk
Installed tk event loop hook.

In [8]: %gui qt
Shell is already running a gui event loop for tk. Call with no arguments to disable the current loop.

In [9]: %gui qt6
Shell is already running a gui event loop for tk. Call with no arguments to disable the current loop.

In [10]: %gui qt5
Shell is already running a gui event loop for tk. Call with no arguments to disable the current loop.

In [11]: %gui
GUI event loop hook for qt5 removed.

In [12]: %gui tk
Installed tk event loop hook.

In [13]: %gui
GUI event loop hook for tk removed.

In [14]: %gui qt5
Cannot switch Qt versions for this session; will use qt6.
Installed qt6 event loop hook.

In [15]: 

This means when you run ipython --matplotlib=tk, for example, you'll see this:

Python 3.10.5 (tags/v3.10.5:f377153, Jun  6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)]
Type 'copyright', 'credits' or 'license' for more information
IPython 8.14.0.dev -- An enhanced Interactive Python. Type '?' for help.
Installed tk event loop hook.

In [1]:

Notes

Working on this has uncovered some interesting dynamics; qt is taken to mean "the latest Qt available" and the current code appears to force, in some cases, what is effectively a %gui qt command before command line or config args are processed (see this issue), so that executing

ipython --matplotlib=qt5

effectively runs

%gui qt
%gui qt5

and if both pyside6 and PyQt5 are installed, the %gui qt5 will trigger a message about not being able to change Qt versions in the session.

[shaperilio]

Removing this import (and the function call that requires it) prevents the unnecessary installation of a qt event loop hook, and as far as I can tell, has no negative effects - I still get inline figures in a Jupyter notebook, for example. I'll need someone with more expertise to chime in on this.