Backport PR #10154: Move ImportDenier to the front of sys.meta_path

Closes gh-9829

IPython/external/qt_loaders.py

@@ -1,296 +1,296 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 sys
 import types
 from functools import partial
 
 from IPython.utils.version import check_version
 
 # Available APIs.
 QT_API_PYQT = 'pyqt' # Force version 2
 QT_API_PYQT5 = 'pyqt5'
 QT_API_PYQTv1 = 'pyqtv1' # Force version 2
 QT_API_PYQT_DEFAULT = 'pyqtdefault' # use system default for version 1 vs. 2
 QT_API_PYSIDE = 'pyside'
 
 
 class ImportDenier(object):
     """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_module(self, fullname, path=None):
         if path:
             return
         if fullname in self.__forbidden:
             return self
 
     def load_module(self, fullname):
         raise ImportError("""
     Importing %s disabled by IPython, which has
     already imported an Incompatible QT Binding: %s
     """ % (fullname, loaded_api()))
 
 ID = ImportDenier()
-sys.meta_path.append(ID)
+sys.meta_path.insert(0, ID)
 
 
 def commit_api(api):
     """Commit to a particular API, and trigger ImportErrors on subsequent
        dangerous imports"""
 
     if api == QT_API_PYSIDE:
         ID.forbid('PyQt4')
         ID.forbid('PyQt5')
     elif api == QT_API_PYQT5:
         ID.forbid('PySide')
         ID.forbid('PyQt4')
     else:   # There are three other possibilities, all representing PyQt4
         ID.forbid('PyQt5')
         ID.forbid('PySide')
 
 
 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, 'pyside', 'pyqt', 'pyqt5', or 'pyqtv1'
     """
     if 'PyQt4.QtCore' in sys.modules:
         if qtapi_version() == 2:
             return QT_API_PYQT
         else:
             return QT_API_PYQTv1
     elif 'PySide.QtCore' in sys.modules:
         return QT_API_PYSIDE
     elif 'PyQt5.QtCore' in sys.modules:
         return QT_API_PYQT5
     return None
 
 
 def has_binding(api):
     """Safely check for PyQt4/5 or PySide, without importing
        submodules
 
        Parameters
        ----------
        api : str [ 'pyqtv1' | 'pyqt' | 'pyqt5' | 'pyside' | 'pyqtdefault']
             Which module to check for
 
        Returns
        -------
        True if the relevant module appears to be importable
     """
     # we can't import an incomplete pyside and pyqt4
     # this will cause a crash in sip (#1431)
     # check for complete presence before importing
     module_name = {QT_API_PYSIDE: 'PySide',
                    QT_API_PYQT: 'PyQt4',
                    QT_API_PYQTv1: 'PyQt4',
                    QT_API_PYQT5: 'PyQt5',
                    QT_API_PYQT_DEFAULT: 'PyQt4'}
     module_name = module_name[api]
 
     import imp
     try:
         #importing top level PyQt4/PySide module is ok...
         mod = __import__(module_name)
         #...importing submodules is not
         imp.find_module('QtCore', mod.__path__)
         imp.find_module('QtGui', mod.__path__)
         imp.find_module('QtSvg', mod.__path__)
         if api == QT_API_PYQT5:
             # QT5 requires QtWidgets too
             imp.find_module('QtWidgets', mod.__path__)
 
         #we can also safely check PySide version
         if api == QT_API_PYSIDE:
             return check_version(mod.__version__, '1.0.3')
         else:
             return True
     except ImportError:
         return False
 
 
 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:
         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_PYQT, QT_API_PYQTv1, 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 rasied 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 not check_version(QtCore.PYQT_VERSION_STR, '4.7'):
         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 rasied within this function are non-recoverable
     """
     import sip
 
     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_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 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',
         '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 becaues they aren't installed, or because
     an incompatible library has already been installed)
     """
     loaders = {QT_API_PYSIDE: import_pyside,
                QT_API_PYQT: import_pyqt4,
                QT_API_PYQT5: import_pyqt5,
                QT_API_PYQTv1: partial(import_pyqt4, version=1),
                QT_API_PYQT_DEFAULT: partial(import_pyqt4, version=None)
                }
 
     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:
         raise ImportError("""
     Could not load requested Qt binding. Please ensure that
     PyQt4 >= 4.7, PyQt5 or PySide >= 1.0.3 is available,
     and only one is imported per session.
 
     Currently-imported Qt library:                              %r
     PyQt4 available (requires QtCore, QtGui, QtSvg):            %s
     PyQt5 available (requires QtCore, QtGui, QtSvg, QtWidgets): %s
     PySide >= 1.0.3 installed:                                  %s
     Tried to load:                                              %r
     """ % (loaded_api(),
            has_binding(QT_API_PYQT),
            has_binding(QT_API_PYQT5),
            has_binding(QT_API_PYSIDE),
            api_options))