Shaperilio/qtgui fixes (#13957)

I started using the released version of my `PySide6`-enabling changes
and noted some problems. In this PR, I fix those, and also overall
improve the feedback to the user when a GUI event loop is hooked in:

- Report which event loop is running when using `%gui <some GUI>`; e.g.
`%gui qt` will show `Installed qt6 event loop hook.`
- Report when the event loop is disabled; i.e. `%gui` will show `GUI
event loop hook disabled.` if an event loop hook was installed, or `No
event loop hook running.` if nothing was installed.
- Requesting a second event loop will give the message `Shell is already
running a gui event loop for <some GUI>. Call with no arguments to
disable current loop.`
- Requesting a different version of Qt, i.e. `%gui qt6` followed by
`%gui` followed by `%gui qt5` will show `Cannot switch Qt versions for
this session; will use qt6.` followed by `Installed qt6 event loop
hook.`

(Fixes / improves  #13864)

IPython/external/qt_loaders.py

@@ -1,405 +1,410 b''
 """
 This module contains factory functions that attempt
 to return Qt submodules from the various python Qt bindings.
 
 It also protects against double-importing Qt with different
 bindings, which is unstable and likely to crash
 
 This is used primarily by qt and qt_for_kernel, and shouldn't
 be accessed directly from the outside
 """
 import importlib.abc
 import sys
+import os
 import types
 from functools import partial, lru_cache
 import operator
 
 # ### Available APIs.
 # Qt6
 QT_API_PYQT6 = "pyqt6"
 QT_API_PYSIDE6 = "pyside6"
 
 # Qt5
 QT_API_PYQT5 = 'pyqt5'
 QT_API_PYSIDE2 = 'pyside2'
 
 # Qt4
 # NOTE: Here for legacy matplotlib compatibility, but not really supported on the IPython side.
 QT_API_PYQT = "pyqt"  # Force version 2
 QT_API_PYQTv1 = "pyqtv1"  # Force version 2
 QT_API_PYSIDE = "pyside"
 
 QT_API_PYQT_DEFAULT = "pyqtdefault"  # use system default for version 1 vs. 2
 
 api_to_module = {
     # Qt6
     QT_API_PYQT6: "PyQt6",
     QT_API_PYSIDE6: "PySide6",
     # Qt5
     QT_API_PYQT5: "PyQt5",
     QT_API_PYSIDE2: "PySide2",
     # Qt4
     QT_API_PYSIDE: "PySide",
     QT_API_PYQT: "PyQt4",
     QT_API_PYQTv1: "PyQt4",
     # default
     QT_API_PYQT_DEFAULT: "PyQt6",
 }
 
 
 class ImportDenier(importlib.abc.MetaPathFinder):
     """Import Hook that will guard against bad Qt imports
     once IPython commits to a specific binding
     """
 
     def __init__(self):
         self.__forbidden = set()
 
     def forbid(self, module_name):
         sys.modules.pop(module_name, None)
         self.__forbidden.add(module_name)
 
     def find_spec(self, fullname, path, target=None):
         if path:
             return
         if fullname in self.__forbidden:
             raise ImportError(
                 """
     Importing %s disabled by IPython, which has
     already imported an Incompatible QT Binding: %s
     """
                 % (fullname, loaded_api())
             )
 
 
 ID = ImportDenier()
 sys.meta_path.insert(0, ID)
 
 
 def commit_api(api):
     """Commit to a particular API, and trigger ImportErrors on subsequent
     dangerous imports"""
     modules = set(api_to_module.values())
 
     modules.remove(api_to_module[api])
     for mod in modules:
         ID.forbid(mod)
 
 
 def loaded_api():
     """Return which API is loaded, if any
 
     If this returns anything besides None,
     importing any other Qt binding is unsafe.
 
     Returns
     -------
     None, 'pyside6', 'pyqt6', 'pyside2', 'pyside', 'pyqt', 'pyqt5', 'pyqtv1'
     """
     if sys.modules.get("PyQt6.QtCore"):
         return QT_API_PYQT6
     elif sys.modules.get("PySide6.QtCore"):
         return QT_API_PYSIDE6
     elif sys.modules.get("PyQt5.QtCore"):
         return QT_API_PYQT5
     elif sys.modules.get("PySide2.QtCore"):
         return QT_API_PYSIDE2
     elif sys.modules.get("PyQt4.QtCore"):
         if qtapi_version() == 2:
             return QT_API_PYQT
         else:
             return QT_API_PYQTv1
     elif sys.modules.get("PySide.QtCore"):
         return QT_API_PYSIDE
 
     return None
 
 
 def has_binding(api):
     """Safely check for PyQt4/5, PySide or PySide2, without importing submodules
 
     Parameters
     ----------
     api : str [ 'pyqtv1' | 'pyqt' | 'pyqt5' | 'pyside' | 'pyside2' | 'pyqtdefault']
         Which module to check for
 
     Returns
     -------
     True if the relevant module appears to be importable
     """
     module_name = api_to_module[api]
     from importlib.util import find_spec
 
     required = ['QtCore', 'QtGui', 'QtSvg']
     if api in (QT_API_PYQT5, QT_API_PYSIDE2, QT_API_PYQT6, QT_API_PYSIDE6):
         # QT5 requires QtWidgets too
         required.append('QtWidgets')
 
     for submod in required:
         try:
             spec = find_spec('%s.%s' % (module_name, submod))
         except ImportError:
             # Package (e.g. PyQt5) not found
             return False
         else:
             if spec is None:
                 # Submodule (e.g. PyQt5.QtCore) not found
                 return False
 
     if api == QT_API_PYSIDE:
         # We can also safely check PySide version
         import PySide
 
         return PySide.__version_info__ >= (1, 0, 3)
 
     return True
 
 
 def qtapi_version():
     """Return which QString API has been set, if any
 
     Returns
     -------
     The QString API version (1 or 2), or None if not set
     """
     try:
         import sip
     except ImportError:
         # as of PyQt5 5.11, sip is no longer available as a top-level
         # module and needs to be imported from the PyQt5 namespace
         try:
             from PyQt5 import sip
         except ImportError:
             return
     try:
         return sip.getapi('QString')
     except ValueError:
         return
 
 
 def can_import(api):
     """Safely query whether an API is importable, without importing it"""
     if not has_binding(api):
         return False
 
     current = loaded_api()
     if api == QT_API_PYQT_DEFAULT:
         return current in [QT_API_PYQT6, None]
     else:
         return current in [api, None]
 
 
 def import_pyqt4(version=2):
     """
     Import PyQt4
 
     Parameters
     ----------
     version : 1, 2, or None
         Which QString/QVariant API to use. Set to None to use the system
         default
     ImportErrors raised within this function are non-recoverable
     """
     # The new-style string API (version=2) automatically
     # converts QStrings to Unicode Python strings. Also, automatically unpacks
     # QVariants to their underlying objects.
     import sip
 
     if version is not None:
         sip.setapi('QString', version)
         sip.setapi('QVariant', version)
 
     from PyQt4 import QtGui, QtCore, QtSvg
 
     if QtCore.PYQT_VERSION < 0x040700:
         raise ImportError("IPython requires PyQt4 >= 4.7, found %s" %
                           QtCore.PYQT_VERSION_STR)
 
     # Alias PyQt-specific functions for PySide compatibility.
     QtCore.Signal = QtCore.pyqtSignal
     QtCore.Slot = QtCore.pyqtSlot
 
     # query for the API version (in case version == None)
     version = sip.getapi('QString')
     api = QT_API_PYQTv1 if version == 1 else QT_API_PYQT
     return QtCore, QtGui, QtSvg, api
 
 
 def import_pyqt5():
     """
     Import PyQt5
 
     ImportErrors raised within this function are non-recoverable
     """
 
     from PyQt5 import QtCore, QtSvg, QtWidgets, QtGui
 
     # Alias PyQt-specific functions for PySide compatibility.
     QtCore.Signal = QtCore.pyqtSignal
     QtCore.Slot = QtCore.pyqtSlot
 
     # Join QtGui and QtWidgets for Qt4 compatibility.
     QtGuiCompat = types.ModuleType('QtGuiCompat')
     QtGuiCompat.__dict__.update(QtGui.__dict__)
     QtGuiCompat.__dict__.update(QtWidgets.__dict__)
 
     api = QT_API_PYQT5
     return QtCore, QtGuiCompat, QtSvg, api
 
 
 def import_pyqt6():
     """
     Import PyQt6
 
     ImportErrors raised within this function are non-recoverable
     """
 
     from PyQt6 import QtCore, QtSvg, QtWidgets, QtGui
 
     # Alias PyQt-specific functions for PySide compatibility.
     QtCore.Signal = QtCore.pyqtSignal
     QtCore.Slot = QtCore.pyqtSlot
 
     # Join QtGui and QtWidgets for Qt4 compatibility.
     QtGuiCompat = types.ModuleType("QtGuiCompat")
     QtGuiCompat.__dict__.update(QtGui.__dict__)
     QtGuiCompat.__dict__.update(QtWidgets.__dict__)
 
     api = QT_API_PYQT6
     return QtCore, QtGuiCompat, QtSvg, api
 
 
 def import_pyside():
     """
     Import PySide
 
     ImportErrors raised within this function are non-recoverable
     """
     from PySide import QtGui, QtCore, QtSvg
     return QtCore, QtGui, QtSvg, QT_API_PYSIDE
 
 def import_pyside2():
     """
     Import PySide2
 
     ImportErrors raised within this function are non-recoverable
     """
     from PySide2 import QtGui, QtCore, QtSvg, QtWidgets, QtPrintSupport
 
     # Join QtGui and QtWidgets for Qt4 compatibility.
     QtGuiCompat = types.ModuleType('QtGuiCompat')
     QtGuiCompat.__dict__.update(QtGui.__dict__)
     QtGuiCompat.__dict__.update(QtWidgets.__dict__)
     QtGuiCompat.__dict__.update(QtPrintSupport.__dict__)
 
     return QtCore, QtGuiCompat, QtSvg, QT_API_PYSIDE2
 
 
 def import_pyside6():
     """
     Import PySide6
 
     ImportErrors raised within this function are non-recoverable
     """
     from PySide6 import QtGui, QtCore, QtSvg, QtWidgets, QtPrintSupport
 
     # Join QtGui and QtWidgets for Qt4 compatibility.
     QtGuiCompat = types.ModuleType("QtGuiCompat")
     QtGuiCompat.__dict__.update(QtGui.__dict__)
     QtGuiCompat.__dict__.update(QtWidgets.__dict__)
     QtGuiCompat.__dict__.update(QtPrintSupport.__dict__)
 
     return QtCore, QtGuiCompat, QtSvg, QT_API_PYSIDE6
 
 
 def load_qt(api_options):
     """
     Attempt to import Qt, given a preference list
     of permissible bindings
 
     It is safe to call this function multiple times.
 
     Parameters
     ----------
     api_options : List of strings
         The order of APIs to try. Valid items are 'pyside', 'pyside2',
         'pyqt', 'pyqt5', 'pyqtv1' and 'pyqtdefault'
 
     Returns
     -------
     A tuple of QtCore, QtGui, QtSvg, QT_API
     The first three are the Qt modules. The last is the
     string indicating which module was loaded.
 
     Raises
     ------
     ImportError, if it isn't possible to import any requested
     bindings (either because they aren't installed, or because
     an incompatible library has already been installed)
     """
     loaders = {
         # Qt6
         QT_API_PYQT6: import_pyqt6,
         QT_API_PYSIDE6: import_pyside6,
         # Qt5
         QT_API_PYQT5: import_pyqt5,
         QT_API_PYSIDE2: import_pyside2,
         # Qt4
         QT_API_PYSIDE: import_pyside,
         QT_API_PYQT: import_pyqt4,
         QT_API_PYQTv1: partial(import_pyqt4, version=1),
         # default
         QT_API_PYQT_DEFAULT: import_pyqt6,
     }
 
     for api in api_options:
 
         if api not in loaders:
             raise RuntimeError(
                 "Invalid Qt API %r, valid values are: %s" %
                 (api, ", ".join(["%r" % k for k in loaders.keys()])))
 
         if not can_import(api):
             continue
 
         #cannot safely recover from an ImportError during this
         result = loaders[api]()
         api = result[-1]  # changed if api = QT_API_PYQT_DEFAULT
         commit_api(api)
         return result
     else:
+        # Clear the environment variable since it doesn't work.
+        if "QT_API" in os.environ:
+            del os.environ["QT_API"]
+
         raise ImportError(
             """
     Could not load requested Qt binding. Please ensure that
     PyQt4 >= 4.7, PyQt5, PyQt6, PySide >= 1.0.3, PySide2, or
     PySide6 is available, and only one is imported per session.
 
     Currently-imported Qt library:                              %r
     PyQt5 available (requires QtCore, QtGui, QtSvg, QtWidgets): %s
     PyQt6 available (requires QtCore, QtGui, QtSvg, QtWidgets): %s
     PySide2 installed:                                          %s
     PySide6 installed:                                          %s
     Tried to load:                                              %r
     """
             % (
                 loaded_api(),
                 has_binding(QT_API_PYQT5),
                 has_binding(QT_API_PYQT6),
                 has_binding(QT_API_PYSIDE2),
                 has_binding(QT_API_PYSIDE6),
                 api_options,
             )
         )
 
 
 def enum_factory(QT_API, QtCore):
     """Construct an enum helper to account for PyQt5 <-> PyQt6 changes."""
 
     @lru_cache(None)
     def _enum(name):
         # foo.bar.Enum.Entry (PyQt6) <=> foo.bar.Entry (non-PyQt6).
         return operator.attrgetter(
             name if QT_API == QT_API_PYQT6 else name.rpartition(".")[0]
         )(sys.modules[QtCore.__package__])
 
     return _enum

IPython/terminal/interactiveshell.py

@@ -1,980 +1,992 b''
 """IPython terminal interface using prompt_toolkit"""
 
 import asyncio
 import os
 import sys
 from warnings import warn
 from typing import Union as UnionType
 
 from IPython.core.async_helpers import get_asyncio_loop
 from IPython.core.interactiveshell import InteractiveShell, InteractiveShellABC
 from IPython.utils.py3compat import input
 from IPython.utils.terminal import toggle_set_term_title, set_term_title, restore_term_title
 from IPython.utils.process import abbrev_cwd
 from traitlets import (
     Bool,
     Unicode,
     Dict,
     Integer,
     List,
     observe,
     Instance,
     Type,
     default,
     Enum,
     Union,
     Any,
     validate,
     Float,
 )
 
 from prompt_toolkit.auto_suggest import AutoSuggestFromHistory
 from prompt_toolkit.enums import DEFAULT_BUFFER, EditingMode
 from prompt_toolkit.filters import HasFocus, Condition, IsDone
 from prompt_toolkit.formatted_text import PygmentsTokens
 from prompt_toolkit.history import History
 from prompt_toolkit.layout.processors import ConditionalProcessor, HighlightMatchingBracketProcessor
 from prompt_toolkit.output import ColorDepth
 from prompt_toolkit.patch_stdout import patch_stdout
 from prompt_toolkit.shortcuts import PromptSession, CompleteStyle, print_formatted_text
 from prompt_toolkit.styles import DynamicStyle, merge_styles
 from prompt_toolkit.styles.pygments import style_from_pygments_cls, style_from_pygments_dict
 from prompt_toolkit import __version__ as ptk_version
 
 from pygments.styles import get_style_by_name
 from pygments.style import Style
 from pygments.token import Token
 
 from .debugger import TerminalPdb, Pdb
 from .magics import TerminalMagics
 from .pt_inputhooks import get_inputhook_name_and_func
 from .prompts import Prompts, ClassicPrompts, RichPromptDisplayHook
 from .ptutils import IPythonPTCompleter, IPythonPTLexer
 from .shortcuts import (
     create_ipython_shortcuts,
     create_identifier,
     RuntimeBinding,
     add_binding,
 )
 from .shortcuts.filters import KEYBINDING_FILTERS, filter_from_string
 from .shortcuts.auto_suggest import (
     NavigableAutoSuggestFromHistory,
     AppendAutoSuggestionInAnyLine,
 )
 
 PTK3 = ptk_version.startswith('3.')
 
 
 class _NoStyle(Style): pass
 
 
 
 _style_overrides_light_bg = {
             Token.Prompt: '#ansibrightblue',
             Token.PromptNum: '#ansiblue bold',
             Token.OutPrompt: '#ansibrightred',
             Token.OutPromptNum: '#ansired bold',
 }
 
 _style_overrides_linux = {
             Token.Prompt: '#ansibrightgreen',
             Token.PromptNum: '#ansigreen bold',
             Token.OutPrompt: '#ansibrightred',
             Token.OutPromptNum: '#ansired bold',
 }
 
 def get_default_editor():
     try:
         return os.environ['EDITOR']
     except KeyError:
         pass
     except UnicodeError:
         warn("$EDITOR environment variable is not pure ASCII. Using platform "
              "default editor.")
 
     if os.name == 'posix':
         return 'vi'  # the only one guaranteed to be there!
     else:
         return 'notepad' # same in Windows!
 
 # conservatively check for tty
 # overridden streams can result in things like:
 # - sys.stdin = None
 # - no isatty method
 for _name in ('stdin', 'stdout', 'stderr'):
     _stream = getattr(sys, _name)
     try:
         if not _stream or not hasattr(_stream, "isatty") or not _stream.isatty():
             _is_tty = False
             break
     except ValueError:
         # stream is closed
         _is_tty = False
         break
 else:
     _is_tty = True
 
 
 _use_simple_prompt = ('IPY_TEST_SIMPLE_PROMPT' in os.environ) or (not _is_tty)
 
 def black_reformat_handler(text_before_cursor):
     """
     We do not need to protect against error,
     this is taken care at a higher level where any reformat error is ignored.
     Indeed we may call reformatting on incomplete code.
     """
     import black
 
     formatted_text = black.format_str(text_before_cursor, mode=black.FileMode())
     if not text_before_cursor.endswith("\n") and formatted_text.endswith("\n"):
         formatted_text = formatted_text[:-1]
     return formatted_text
 
 
 def yapf_reformat_handler(text_before_cursor):
     from yapf.yapflib import file_resources
     from yapf.yapflib import yapf_api
 
     style_config = file_resources.GetDefaultStyleForDir(os.getcwd())
     formatted_text, was_formatted = yapf_api.FormatCode(
         text_before_cursor, style_config=style_config
     )
     if was_formatted:
         if not text_before_cursor.endswith("\n") and formatted_text.endswith("\n"):
             formatted_text = formatted_text[:-1]
         return formatted_text
     else:
         return text_before_cursor
 
 
 class PtkHistoryAdapter(History):
     """
     Prompt toolkit has it's own way of handling history, Where it assumes it can
     Push/pull from history.
 
     """
 
     def __init__(self, shell):
         super().__init__()
         self.shell = shell
         self._refresh()
 
     def append_string(self, string):
         # we rely on sql for that.
         self._loaded = False
         self._refresh()
 
     def _refresh(self):
         if not self._loaded:
             self._loaded_strings = list(self.load_history_strings())
 
     def load_history_strings(self):
         last_cell = ""
         res = []
         for __, ___, cell in self.shell.history_manager.get_tail(
             self.shell.history_load_length, include_latest=True
         ):
             # Ignore blank lines and consecutive duplicates
             cell = cell.rstrip()
             if cell and (cell != last_cell):
                 res.append(cell)
                 last_cell = cell
         yield from res[::-1]
 
     def store_string(self, string: str) -> None:
         pass
 
 class TerminalInteractiveShell(InteractiveShell):
     mime_renderers = Dict().tag(config=True)
 
     space_for_menu = Integer(6, help='Number of line at the bottom of the screen '
                                      'to reserve for the tab completion menu, '
                                      'search history, ...etc, the height of '
                                      'these menus will at most this value. '
                                      'Increase it is you prefer long and skinny '
                                      'menus, decrease for short and wide.'
                             ).tag(config=True)
 
     pt_app: UnionType[PromptSession, None] = None
     auto_suggest: UnionType[
         AutoSuggestFromHistory, NavigableAutoSuggestFromHistory, None
     ] = None
     debugger_history = None
 
     debugger_history_file = Unicode(
         "~/.pdbhistory", help="File in which to store and read history"
     ).tag(config=True)
 
     simple_prompt = Bool(_use_simple_prompt,
         help="""Use `raw_input` for the REPL, without completion and prompt colors.
 
             Useful when controlling IPython as a subprocess, and piping STDIN/OUT/ERR. Known usage are:
             IPython own testing machinery, and emacs inferior-shell integration through elpy.
 
             This mode default to `True` if the `IPY_TEST_SIMPLE_PROMPT`
             environment variable is set, or the current terminal is not a tty."""
             ).tag(config=True)
 
     @property
     def debugger_cls(self):
         return Pdb if self.simple_prompt else TerminalPdb
 
     confirm_exit = Bool(True,
         help="""
         Set to confirm when you try to exit IPython with an EOF (Control-D
         in Unix, Control-Z/Enter in Windows). By typing 'exit' or 'quit',
         you can force a direct exit without any confirmation.""",
     ).tag(config=True)
 
     editing_mode = Unicode('emacs',
         help="Shortcut style to use at the prompt. 'vi' or 'emacs'.",
     ).tag(config=True)
 
     emacs_bindings_in_vi_insert_mode = Bool(
         True,
         help="Add shortcuts from 'emacs' insert mode to 'vi' insert mode.",
     ).tag(config=True)
 
     modal_cursor = Bool(
         True,
         help="""
        Cursor shape changes depending on vi mode: beam in vi insert mode,
        block in nav mode, underscore in replace mode.""",
     ).tag(config=True)
 
     ttimeoutlen = Float(
         0.01,
         help="""The time in milliseconds that is waited for a key code
        to complete.""",
     ).tag(config=True)
 
     timeoutlen = Float(
         0.5,
         help="""The time in milliseconds that is waited for a mapped key
        sequence to complete.""",
     ).tag(config=True)
 
     autoformatter = Unicode(
         None,
         help="Autoformatter to reformat Terminal code. Can be `'black'`, `'yapf'` or `None`",
         allow_none=True
     ).tag(config=True)
 
     auto_match = Bool(
         False,
         help="""
         Automatically add/delete closing bracket or quote when opening bracket or quote is entered/deleted.
         Brackets: (), [], {}
         Quotes: '', \"\"
         """,
     ).tag(config=True)
 
     mouse_support = Bool(False,
         help="Enable mouse support in the prompt\n(Note: prevents selecting text with the mouse)"
     ).tag(config=True)
 
     # We don't load the list of styles for the help string, because loading
     # Pygments plugins takes time and can cause unexpected errors.
     highlighting_style = Union([Unicode('legacy'), Type(klass=Style)],
         help="""The name or class of a Pygments style to use for syntax
         highlighting. To see available styles, run `pygmentize -L styles`."""
     ).tag(config=True)
 
     @validate('editing_mode')
     def _validate_editing_mode(self, proposal):
         if proposal['value'].lower() == 'vim':
             proposal['value']= 'vi'
         elif proposal['value'].lower() == 'default':
             proposal['value']= 'emacs'
 
         if hasattr(EditingMode, proposal['value'].upper()):
             return proposal['value'].lower()
 
         return self.editing_mode
 
 
     @observe('editing_mode')
     def _editing_mode(self, change):
         if self.pt_app:
             self.pt_app.editing_mode = getattr(EditingMode, change.new.upper())
 
     def _set_formatter(self, formatter):
         if formatter is None:
             self.reformat_handler = lambda x:x
         elif formatter == 'black':
             self.reformat_handler = black_reformat_handler
         elif formatter == "yapf":
             self.reformat_handler = yapf_reformat_handler
         else:
             raise ValueError
 
     @observe("autoformatter")
     def _autoformatter_changed(self, change):
         formatter = change.new
         self._set_formatter(formatter)
 
     @observe('highlighting_style')
     @observe('colors')
     def _highlighting_style_changed(self, change):
         self.refresh_style()
 
     def refresh_style(self):
         self._style = self._make_style_from_name_or_cls(self.highlighting_style)
 
 
     highlighting_style_overrides = Dict(
         help="Override highlighting format for specific tokens"
     ).tag(config=True)
 
     true_color = Bool(False,
         help="""Use 24bit colors instead of 256 colors in prompt highlighting.
         If your terminal supports true color, the following command should
         print ``TRUECOLOR`` in orange::
 
             printf \"\\x1b[38;2;255;100;0mTRUECOLOR\\x1b[0m\\n\"
         """,
     ).tag(config=True)
 
     editor = Unicode(get_default_editor(),
         help="Set the editor used by IPython (default to $EDITOR/vi/notepad)."
     ).tag(config=True)
 
     prompts_class = Type(Prompts, help='Class used to generate Prompt token for prompt_toolkit').tag(config=True)
 
     prompts = Instance(Prompts)
 
     @default('prompts')
     def _prompts_default(self):
         return self.prompts_class(self)
 
 #    @observe('prompts')
 #    def _(self, change):
 #        self._update_layout()
 
     @default('displayhook_class')
     def _displayhook_class_default(self):
         return RichPromptDisplayHook
 
     term_title = Bool(True,
         help="Automatically set the terminal title"
     ).tag(config=True)
 
     term_title_format = Unicode("IPython: {cwd}",
         help="Customize the terminal title format.  This is a python format string. " +
              "Available substitutions are: {cwd}."
     ).tag(config=True)
 
     display_completions = Enum(('column', 'multicolumn','readlinelike'),
         help= ( "Options for displaying tab completions, 'column', 'multicolumn', and "
                 "'readlinelike'. These options are for `prompt_toolkit`, see "
                 "`prompt_toolkit` documentation for more information."
                 ),
         default_value='multicolumn').tag(config=True)
 
     highlight_matching_brackets = Bool(True,
         help="Highlight matching brackets.",
     ).tag(config=True)
 
     extra_open_editor_shortcuts = Bool(False,
         help="Enable vi (v) or Emacs (C-X C-E) shortcuts to open an external editor. "
              "This is in addition to the F2 binding, which is always enabled."
     ).tag(config=True)
 
     handle_return = Any(None,
         help="Provide an alternative handler to be called when the user presses "
              "Return. This is an advanced option intended for debugging, which "
              "may be changed or removed in later releases."
     ).tag(config=True)
 
     enable_history_search = Bool(True,
         help="Allows to enable/disable the prompt toolkit history search"
     ).tag(config=True)
 
     autosuggestions_provider = Unicode(
         "NavigableAutoSuggestFromHistory",
         help="Specifies from which source automatic suggestions are provided. "
         "Can be set to ``'NavigableAutoSuggestFromHistory'`` (:kbd:`up` and "
         ":kbd:`down` swap suggestions), ``'AutoSuggestFromHistory'``, "
         " or ``None`` to disable automatic suggestions. "
         "Default is `'NavigableAutoSuggestFromHistory`'.",
         allow_none=True,
     ).tag(config=True)
 
     def _set_autosuggestions(self, provider):
         # disconnect old handler
         if self.auto_suggest and isinstance(
             self.auto_suggest, NavigableAutoSuggestFromHistory
         ):
             self.auto_suggest.disconnect()
         if provider is None:
             self.auto_suggest = None
         elif provider == "AutoSuggestFromHistory":
             self.auto_suggest = AutoSuggestFromHistory()
         elif provider == "NavigableAutoSuggestFromHistory":
             self.auto_suggest = NavigableAutoSuggestFromHistory()
         else:
             raise ValueError("No valid provider.")
         if self.pt_app:
             self.pt_app.auto_suggest = self.auto_suggest
 
     @observe("autosuggestions_provider")
     def _autosuggestions_provider_changed(self, change):
         provider = change.new
         self._set_autosuggestions(provider)
 
     shortcuts = List(
         trait=Dict(
             key_trait=Enum(
                 [
                     "command",
                     "match_keys",
                     "match_filter",
                     "new_keys",
                     "new_filter",
                     "create",
                 ]
             ),
             per_key_traits={
                 "command": Unicode(),
                 "match_keys": List(Unicode()),
                 "match_filter": Unicode(),
                 "new_keys": List(Unicode()),
                 "new_filter": Unicode(),
                 "create": Bool(False),
             },
         ),
         help="""Add, disable or modifying shortcuts.
 
         Each entry on the list should be a dictionary with ``command`` key
         identifying the target function executed by the shortcut and at least
         one of the following:
 
         - ``match_keys``: list of keys used to match an existing shortcut,
         - ``match_filter``: shortcut filter used to match an existing shortcut,
         - ``new_keys``: list of keys to set,
         - ``new_filter``: a new shortcut filter to set
 
         The filters have to be composed of pre-defined verbs and joined by one
         of the following conjunctions: ``&`` (and), ``|`` (or), ``~`` (not).
         The pre-defined verbs are:
 
         {}
 
 
         To disable a shortcut set ``new_keys`` to an empty list.
         To add a shortcut add key ``create`` with value ``True``.
 
         When modifying/disabling shortcuts, ``match_keys``/``match_filter`` can
         be omitted if the provided specification uniquely identifies a shortcut
         to be modified/disabled. When modifying a shortcut ``new_filter`` or
         ``new_keys`` can be omitted which will result in reuse of the existing
         filter/keys.
 
         Only shortcuts defined in IPython (and not default prompt-toolkit
         shortcuts) can be modified or disabled. The full list of shortcuts,
         command identifiers and filters is available under
         :ref:`terminal-shortcuts-list`.
         """.format(
             "\n        ".join([f"- `{k}`" for k in KEYBINDING_FILTERS])
         ),
     ).tag(config=True)
 
     @observe("shortcuts")
     def _shortcuts_changed(self, change):
         if self.pt_app:
             self.pt_app.key_bindings = self._merge_shortcuts(user_shortcuts=change.new)
 
     def _merge_shortcuts(self, user_shortcuts):
         # rebuild the bindings list from scratch
         key_bindings = create_ipython_shortcuts(self)
 
         # for now we only allow adding shortcuts for commands which are already
         # registered; this is a security precaution.
         known_commands = {
             create_identifier(binding.handler): binding.handler
             for binding in key_bindings.bindings
         }
         shortcuts_to_skip = []
         shortcuts_to_add = []
 
         for shortcut in user_shortcuts:
             command_id = shortcut["command"]
             if command_id not in known_commands:
                 allowed_commands = "\n - ".join(known_commands)
                 raise ValueError(
                     f"{command_id} is not a known shortcut command."
                     f" Allowed commands are: \n - {allowed_commands}"
                 )
             old_keys = shortcut.get("match_keys", None)
             old_filter = (
                 filter_from_string(shortcut["match_filter"])
                 if "match_filter" in shortcut
                 else None
             )
             matching = [
                 binding
                 for binding in key_bindings.bindings
                 if (
                     (old_filter is None or binding.filter == old_filter)
                     and (old_keys is None or [k for k in binding.keys] == old_keys)
                     and create_identifier(binding.handler) == command_id
                 )
             ]
 
             new_keys = shortcut.get("new_keys", None)
             new_filter = shortcut.get("new_filter", None)
 
             command = known_commands[command_id]
 
             creating_new = shortcut.get("create", False)
             modifying_existing = not creating_new and (
                 new_keys is not None or new_filter
             )
 
             if creating_new and new_keys == []:
                 raise ValueError("Cannot add a shortcut without keys")
 
             if modifying_existing:
                 specification = {
                     key: shortcut[key]
                     for key in ["command", "filter"]
                     if key in shortcut
                 }
                 if len(matching) == 0:
                     raise ValueError(
                         f"No shortcuts matching {specification} found in {key_bindings.bindings}"
                     )
                 elif len(matching) > 1:
                     raise ValueError(
                         f"Multiple shortcuts matching {specification} found,"
                         f" please add keys/filter to select one of: {matching}"
                     )
 
                 matched = matching[0]
                 old_filter = matched.filter
                 old_keys = list(matched.keys)
                 shortcuts_to_skip.append(
                     RuntimeBinding(
                         command,
                         keys=old_keys,
                         filter=old_filter,
                     )
                 )
 
             if new_keys != []:
                 shortcuts_to_add.append(
                     RuntimeBinding(
                         command,
                         keys=new_keys or old_keys,
                         filter=filter_from_string(new_filter)
                         if new_filter is not None
                         else (
                             old_filter
                             if old_filter is not None
                             else filter_from_string("always")
                         ),
                     )
                 )
 
         # rebuild the bindings list from scratch
         key_bindings = create_ipython_shortcuts(self, skip=shortcuts_to_skip)
         for binding in shortcuts_to_add:
             add_binding(key_bindings, binding)
 
         return key_bindings
 
     prompt_includes_vi_mode = Bool(True,
         help="Display the current vi mode (when using vi editing mode)."
     ).tag(config=True)
 
     @observe('term_title')
     def init_term_title(self, change=None):
         # Enable or disable the terminal title.
         if self.term_title and _is_tty:
             toggle_set_term_title(True)
             set_term_title(self.term_title_format.format(cwd=abbrev_cwd()))
         else:
             toggle_set_term_title(False)
 
     def restore_term_title(self):
         if self.term_title and _is_tty:
             restore_term_title()
 
     def init_display_formatter(self):
         super(TerminalInteractiveShell, self).init_display_formatter()
         # terminal only supports plain text
         self.display_formatter.active_types = ["text/plain"]
 
     def init_prompt_toolkit_cli(self):
         if self.simple_prompt:
             # Fall back to plain non-interactive output for tests.
             # This is very limited.
             def prompt():
                 prompt_text = "".join(x[1] for x in self.prompts.in_prompt_tokens())
                 lines = [input(prompt_text)]
                 prompt_continuation = "".join(x[1] for x in self.prompts.continuation_prompt_tokens())
                 while self.check_complete('\n'.join(lines))[0] == 'incomplete':
                     lines.append( input(prompt_continuation) )
                 return '\n'.join(lines)
             self.prompt_for_code = prompt
             return
 
         # Set up keyboard shortcuts
         key_bindings = self._merge_shortcuts(user_shortcuts=self.shortcuts)
 
         # Pre-populate history from IPython's history database
         history = PtkHistoryAdapter(self)
 
         self._style = self._make_style_from_name_or_cls(self.highlighting_style)
         self.style = DynamicStyle(lambda: self._style)
 
         editing_mode = getattr(EditingMode, self.editing_mode.upper())
 
         self.pt_loop = asyncio.new_event_loop()
         self.pt_app = PromptSession(
             auto_suggest=self.auto_suggest,
             editing_mode=editing_mode,
             key_bindings=key_bindings,
             history=history,
             completer=IPythonPTCompleter(shell=self),
             enable_history_search=self.enable_history_search,
             style=self.style,
             include_default_pygments_style=False,
             mouse_support=self.mouse_support,
             enable_open_in_editor=self.extra_open_editor_shortcuts,
             color_depth=self.color_depth,
             tempfile_suffix=".py",
             **self._extra_prompt_options(),
         )
         if isinstance(self.auto_suggest, NavigableAutoSuggestFromHistory):
             self.auto_suggest.connect(self.pt_app)
 
     def _make_style_from_name_or_cls(self, name_or_cls):
         """
         Small wrapper that make an IPython compatible style from a style name
 
         We need that to add style for prompt ... etc.
         """
         style_overrides = {}
         if name_or_cls == 'legacy':
             legacy = self.colors.lower()
             if legacy == 'linux':
                 style_cls = get_style_by_name('monokai')
                 style_overrides = _style_overrides_linux
             elif legacy == 'lightbg':
                 style_overrides = _style_overrides_light_bg
                 style_cls = get_style_by_name('pastie')
             elif legacy == 'neutral':
                 # The default theme needs to be visible on both a dark background
                 # and a light background, because we can't tell what the terminal
                 # looks like. These tweaks to the default theme help with that.
                 style_cls = get_style_by_name('default')
                 style_overrides.update({
                     Token.Number: '#ansigreen',
                     Token.Operator: 'noinherit',
                     Token.String: '#ansiyellow',
                     Token.Name.Function: '#ansiblue',
                     Token.Name.Class: 'bold #ansiblue',
                     Token.Name.Namespace: 'bold #ansiblue',
                     Token.Name.Variable.Magic: '#ansiblue',
                     Token.Prompt: '#ansigreen',
                     Token.PromptNum: '#ansibrightgreen bold',
                     Token.OutPrompt: '#ansired',
                     Token.OutPromptNum: '#ansibrightred bold',
                 })
 
                 # Hack: Due to limited color support on the Windows console
                 # the prompt colors will be wrong without this
                 if os.name == 'nt':
                     style_overrides.update({
                         Token.Prompt: '#ansidarkgreen',
                         Token.PromptNum: '#ansigreen bold',
                         Token.OutPrompt: '#ansidarkred',
                         Token.OutPromptNum: '#ansired bold',
                     })
             elif legacy =='nocolor':
                 style_cls=_NoStyle
                 style_overrides = {}
             else :
                 raise ValueError('Got unknown colors: ', legacy)
         else :
             if isinstance(name_or_cls, str):
                 style_cls = get_style_by_name(name_or_cls)
             else:
                 style_cls = name_or_cls
             style_overrides = {
                 Token.Prompt: '#ansigreen',
                 Token.PromptNum: '#ansibrightgreen bold',
                 Token.OutPrompt: '#ansired',
                 Token.OutPromptNum: '#ansibrightred bold',
             }
         style_overrides.update(self.highlighting_style_overrides)
         style = merge_styles([
             style_from_pygments_cls(style_cls),
             style_from_pygments_dict(style_overrides),
         ])
 
         return style
 
     @property
     def pt_complete_style(self):
         return {
             'multicolumn': CompleteStyle.MULTI_COLUMN,
             'column': CompleteStyle.COLUMN,
             'readlinelike': CompleteStyle.READLINE_LIKE,
         }[self.display_completions]
 
     @property
     def color_depth(self):
         return (ColorDepth.TRUE_COLOR if self.true_color else None)
 
     def _extra_prompt_options(self):
         """
         Return the current layout option for the current Terminal InteractiveShell
         """
         def get_message():
             return PygmentsTokens(self.prompts.in_prompt_tokens())
 
         if self.editing_mode == 'emacs':
             # with emacs mode the prompt is (usually) static, so we call only
             # the function once. With VI mode it can toggle between [ins] and
             # [nor] so we can't precompute.
             # here I'm going to favor the default keybinding which almost
             # everybody uses to decrease CPU usage.
             # if we have issues with users with custom Prompts we can see how to
             # work around this.
             get_message = get_message()
 
         options = {
             "complete_in_thread": False,
             "lexer": IPythonPTLexer(),
             "reserve_space_for_menu": self.space_for_menu,
             "message": get_message,
             "prompt_continuation": (
                 lambda width, lineno, is_soft_wrap: PygmentsTokens(
                     self.prompts.continuation_prompt_tokens(width)
                 )
             ),
             "multiline": True,
             "complete_style": self.pt_complete_style,
             "input_processors": [
                 # Highlight matching brackets, but only when this setting is
                 # enabled, and only when the DEFAULT_BUFFER has the focus.
                 ConditionalProcessor(
                     processor=HighlightMatchingBracketProcessor(chars="[](){}"),
                     filter=HasFocus(DEFAULT_BUFFER)
                     & ~IsDone()
                     & Condition(lambda: self.highlight_matching_brackets),
                 ),
                 # Show auto-suggestion in lines other than the last line.
                 ConditionalProcessor(
                     processor=AppendAutoSuggestionInAnyLine(),
                     filter=HasFocus(DEFAULT_BUFFER)
                     & ~IsDone()
                     & Condition(
                         lambda: isinstance(
                             self.auto_suggest, NavigableAutoSuggestFromHistory
                         )
                     ),
                 ),
             ],
         }
         if not PTK3:
             options['inputhook'] = self.inputhook
 
         return options
 
     def prompt_for_code(self):
         if self.rl_next_input:
             default = self.rl_next_input
             self.rl_next_input = None
         else:
             default = ''
 
         # In order to make sure that asyncio code written in the
         # interactive shell doesn't interfere with the prompt, we run the
         # prompt in a different event loop.
         # If we don't do this, people could spawn coroutine with a
         # while/true inside which will freeze the prompt.
 
         policy = asyncio.get_event_loop_policy()
         old_loop = get_asyncio_loop()
 
         # FIXME: prompt_toolkit is using the deprecated `asyncio.get_event_loop`
         # to get the current event loop.
         # This will probably be replaced by an attribute or input argument,
         # at which point we can stop calling the soon-to-be-deprecated `set_event_loop` here.
         if old_loop is not self.pt_loop:
             policy.set_event_loop(self.pt_loop)
         try:
             with patch_stdout(raw=True):
                 text = self.pt_app.prompt(
                     default=default,
                     **self._extra_prompt_options())
         finally:
             # Restore the original event loop.
             if old_loop is not None and old_loop is not self.pt_loop:
                 policy.set_event_loop(old_loop)
 
         return text
 
     def enable_win_unicode_console(self):
         # Since IPython 7.10 doesn't support python < 3.6 and PEP 528, Python uses the unicode APIs for the Windows
         # console by default, so WUC shouldn't be needed.
         warn("`enable_win_unicode_console` is deprecated since IPython 7.10, does not do anything and will be removed in the future",
              DeprecationWarning,
              stacklevel=2)
 
     def init_io(self):
         if sys.platform not in {'win32', 'cli'}:
             return
 
         import colorama
         colorama.init()
 
     def init_magics(self):
         super(TerminalInteractiveShell, self).init_magics()
         self.register_magics(TerminalMagics)
 
     def init_alias(self):
         # The parent class defines aliases that can be safely used with any
         # frontend.
         super(TerminalInteractiveShell, self).init_alias()
 
         # Now define aliases that only make sense on the terminal, because they
         # need direct access to the console in a way that we can't emulate in
         # GUI or web frontend
         if os.name == 'posix':
             for cmd in ('clear', 'more', 'less', 'man'):
                 self.alias_manager.soft_define_alias(cmd, cmd)
 
 
     def __init__(self, *args, **kwargs) -> None:
         super(TerminalInteractiveShell, self).__init__(*args, **kwargs)
         self._set_autosuggestions(self.autosuggestions_provider)
         self.init_prompt_toolkit_cli()
         self.init_term_title()
         self.keep_running = True
         self._set_formatter(self.autoformatter)
 
 
     def ask_exit(self):
         self.keep_running = False
 
     rl_next_input = None
 
     def interact(self):
         self.keep_running = True
         while self.keep_running:
             print(self.separate_in, end='')
 
             try:
                 code = self.prompt_for_code()
             except EOFError:
                 if (not self.confirm_exit) \
                         or self.ask_yes_no('Do you really want to exit ([y]/n)?','y','n'):
                     self.ask_exit()
 
             else:
                 if code:
                     self.run_cell(code, store_history=True)
 
     def mainloop(self):
         # An extra layer of protection in case someone mashing Ctrl-C breaks
         # out of our internal code.
         while True:
             try:
                 self.interact()
                 break
             except KeyboardInterrupt as e:
                 print("\n%s escaped interact()\n" % type(e).__name__)
             finally:
                 # An interrupt during the eventloop will mess up the
                 # internal state of the prompt_toolkit library.
                 # Stopping the eventloop fixes this, see
                 # https://github.com/ipython/ipython/pull/9867
                 if hasattr(self, '_eventloop'):
                     self._eventloop.stop()
 
                 self.restore_term_title()
 
         # try to call some at-exit operation optimistically as some things can't
         # be done during interpreter shutdown. this is technically inaccurate as
         # this make mainlool not re-callable, but that should be a rare if not
         # in existent use case.
 
         self._atexit_once()
 
 
     _inputhook = None
     def inputhook(self, context):
         if self._inputhook is not None:
             self._inputhook(context)
 
     active_eventloop = None
     def enable_gui(self, gui=None):
+        if self._inputhook is None and gui is None:
+            print("No event loop hook running.")
+            return
+
         if self._inputhook is not None and gui is not None:
-            warn(
-                f"Shell was already running a gui event loop for {self.active_eventloop}; switching to {gui}."
+            print(
+                f"Shell is already running a gui event loop for {self.active_eventloop}. "
+                "Call with no arguments to disable the current loop."
             )
+            return
+        if self._inputhook is not None and gui is None:
+            self.active_eventloop = self._inputhook = None
+
         if gui and (gui not in {"inline", "webagg"}):
             # This hook runs with each cycle of the `prompt_toolkit`'s event loop.
             self.active_eventloop, self._inputhook = get_inputhook_name_and_func(gui)
         else:
             self.active_eventloop = self._inputhook = None
 
         # For prompt_toolkit 3.0. We have to create an asyncio event loop with
         # this inputhook.
         if PTK3:
             import asyncio
             from prompt_toolkit.eventloop import new_eventloop_with_inputhook
 
             if gui == 'asyncio':
                 # When we integrate the asyncio event loop, run the UI in the
                 # same event loop as the rest of the code. don't use an actual
                 # input hook. (Asyncio is not made for nesting event loops.)
                 self.pt_loop = get_asyncio_loop()
+                print("Installed asyncio event loop hook.")
 
             elif self._inputhook:
                 # If an inputhook was set, create a new asyncio event loop with
                 # this inputhook for the prompt.
                 self.pt_loop = new_eventloop_with_inputhook(self._inputhook)
+                print(f"Installed {self.active_eventloop} event loop hook.")
             else:
                 # When there's no inputhook, run the prompt in a separate
                 # asyncio event loop.
                 self.pt_loop = asyncio.new_event_loop()
+                print("GUI event loop hook disabled.")
 
     # Run !system commands directly, not through pipes, so terminal programs
     # work correctly.
     system = InteractiveShell.system_raw
 
     def auto_rewrite_input(self, cmd):
         """Overridden from the parent class to use fancy rewriting prompt"""
         if not self.show_rewritten_input:
             return
 
         tokens = self.prompts.rewrite_prompt_tokens()
         if self.pt_app:
             print_formatted_text(PygmentsTokens(tokens), end='',
                                  style=self.pt_app.app.style)
             print(cmd)
         else:
             prompt = ''.join(s for t, s in tokens)
             print(prompt, cmd, sep='')
 
     _prompts_before = None
     def switch_doctest_mode(self, mode):
         """Switch prompts to classic for %doctest_mode"""
         if mode:
             self._prompts_before = self.prompts
             self.prompts = ClassicPrompts(self)
         elif self._prompts_before:
             self.prompts = self._prompts_before
             self._prompts_before = None
 #        self._update_layout()
 
 
 InteractiveShellABC.register(TerminalInteractiveShell)
 
 if __name__ == '__main__':
     TerminalInteractiveShell.instance().interact()

IPython/terminal/pt_inputhooks/__init__.py

@@ -1,132 +1,138 b''
 import importlib
 import os
 
 aliases = {
     'qt4': 'qt',
     'gtk2': 'gtk',
 }
 
 backends = [
     "qt",
     "qt5",
     "qt6",
     "gtk",
     "gtk2",
     "gtk3",
     "gtk4",
     "tk",
     "wx",
     "pyglet",
     "glut",
     "osx",
     "asyncio",
 ]
 
 registered = {}
 
 def register(name, inputhook):
     """Register the function *inputhook* as an event loop integration."""
     registered[name] = inputhook
 
 
 class UnknownBackend(KeyError):
     def __init__(self, name):
         self.name = name
 
     def __str__(self):
         return ("No event loop integration for {!r}. "
                 "Supported event loops are: {}").format(self.name,
                                     ', '.join(backends + sorted(registered)))
 
 
 def set_qt_api(gui):
     """Sets the `QT_API` environment variable if it isn't already set."""
 
     qt_api = os.environ.get("QT_API", None)
 
     from IPython.external.qt_loaders import (
         QT_API_PYQT,
         QT_API_PYQT5,
         QT_API_PYQT6,
         QT_API_PYSIDE,
         QT_API_PYSIDE2,
         QT_API_PYSIDE6,
         QT_API_PYQTv1,
         loaded_api,
     )
 
     loaded = loaded_api()
 
     qt_env2gui = {
         QT_API_PYSIDE: "qt4",
         QT_API_PYQTv1: "qt4",
         QT_API_PYQT: "qt4",
         QT_API_PYSIDE2: "qt5",
         QT_API_PYQT5: "qt5",
         QT_API_PYSIDE6: "qt6",
         QT_API_PYQT6: "qt6",
     }
     if loaded is not None and gui != "qt":
         if qt_env2gui[loaded] != gui:
             print(
-                f"Cannot switch Qt versions for this session; must use {qt_env2gui[loaded]}."
+                f"Cannot switch Qt versions for this session; will use {qt_env2gui[loaded]}."
             )
-            return
+            return qt_env2gui[loaded]
 
     if qt_api is not None and gui != "qt":
         if qt_env2gui[qt_api] != gui:
             print(
                 f'Request for "{gui}" will be ignored because `QT_API` '
                 f'environment variable is set to "{qt_api}"'
             )
+            return qt_env2gui[qt_api]
     else:
         if gui == "qt5":
             try:
                 import PyQt5  # noqa
 
                 os.environ["QT_API"] = "pyqt5"
             except ImportError:
                 try:
                     import PySide2  # noqa
 
                     os.environ["QT_API"] = "pyside2"
                 except ImportError:
                     os.environ["QT_API"] = "pyqt5"
         elif gui == "qt6":
             try:
                 import PyQt6  # noqa
 
                 os.environ["QT_API"] = "pyqt6"
             except ImportError:
                 try:
                     import PySide6  # noqa
 
                     os.environ["QT_API"] = "pyside6"
                 except ImportError:
                     os.environ["QT_API"] = "pyqt6"
         elif gui == "qt":
             # Don't set QT_API; let IPython logic choose the version.
             if "QT_API" in os.environ.keys():
                 del os.environ["QT_API"]
         else:
             print(f'Unrecognized Qt version: {gui}. Should be "qt5", "qt6", or "qt".')
             return
 
+        # Import it now so we can figure out which version it is.
+        from IPython.external.qt_for_kernel import QT_API
+
+        return qt_env2gui[QT_API]
+
 
 def get_inputhook_name_and_func(gui):
     if gui in registered:
         return gui, registered[gui]
 
     if gui not in backends:
         raise UnknownBackend(gui)
 
     if gui in aliases:
         return get_inputhook_name_and_func(aliases[gui])
 
     gui_mod = gui
     if gui.startswith("qt"):
-        set_qt_api(gui)
+        gui = set_qt_api(gui)
         gui_mod = "qt"
 
     mod = importlib.import_module("IPython.terminal.pt_inputhooks." + gui_mod)
     return gui, mod.inputhook

IPython/terminal/tests/test_pt_inputhooks.py

@@ -1,50 +1,50 b''
 import os
 import importlib
 
 import pytest
 
 from IPython.terminal.pt_inputhooks import set_qt_api, get_inputhook_name_and_func
 
 
 guis_avail = []
 
 
 def _get_qt_vers():
     """If any version of Qt is available, this will populate `guis_avail` with 'qt' and 'qtx'. Due
     to the import mechanism, we can't import multiple versions of Qt in one session."""
     for gui in ["qt", "qt6", "qt5"]:
         print(f"Trying {gui}")
         try:
             set_qt_api(gui)
             importlib.import_module("IPython.terminal.pt_inputhooks.qt")
             guis_avail.append(gui)
             if "QT_API" in os.environ.keys():
                 del os.environ["QT_API"]
         except ImportError:
             pass  # that version of Qt isn't available.
         except RuntimeError:
             pass  # the version of IPython doesn't know what to do with this Qt version.
 
 
 _get_qt_vers()
 
 
 @pytest.mark.skipif(
     len(guis_avail) == 0, reason="No viable version of PyQt or PySide installed."
 )
 def test_inputhook_qt():
-    gui = guis_avail[0]
-
-    # Choose a qt version and get the input hook function. This will import Qt...
-    get_inputhook_name_and_func(gui)
-
-    # ...and now we're stuck with this version of Qt for good; can't switch.
-    for not_gui in ["qt6", "qt5"]:
-        if not_gui not in guis_avail:
-            break
-
-    with pytest.raises(ImportError):
-        get_inputhook_name_and_func(not_gui)
-
-    # A gui of 'qt' means "best available", or in this case, the last one that was used.
-    get_inputhook_name_and_func("qt")
+    # Choose the "best" Qt version.
+    gui_ret, _ = get_inputhook_name_and_func("qt")
+
+    assert gui_ret != "qt"  # you get back the specific version that was loaded.
+    assert gui_ret in guis_avail
+
+    if len(guis_avail) > 2:
+        # ...and now we're stuck with this version of Qt for good; can't switch.
+        for not_gui in ["qt6", "qt5"]:
+            if not_gui != gui_ret:
+                break
+        # Try to import the other gui; it won't work.
+        gui_ret2, _ = get_inputhook_name_and_func(not_gui)
+        assert gui_ret2 == gui_ret
+        assert gui_ret2 != not_gui