Refactor qt import logic. Fixes #2955

IPython/external/qt_loaders.py

@@ -0,0 +1,238 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
+from functools import partial
+
+from IPython.utils.version import check_version
+
+# Available APIs.
+QT_API_PYQT = 'pyqt'
+QT_API_PYQTv1 = 'pyqtv1'
+QT_API_PYSIDE = 'pyside'
+
+
+class ImportDenier(object):
+    """Import Hook that will guard against bad Qt imports
+    once IPython commits to a specific binding
+    """
+    __forbidden = set()
+
+    def __init__(self):
+        self.__forbidden = None
+
+    def forbid(self, module_name):
+        sys.modules.pop(module_name, None)
+        self.__forbidden = module_name
+
+    def find_module(self, mod_name, pth):
+        if pth:
+            return
+        if mod_name == self.__forbidden:
+            return self
+
+    def load_module(self, mod_name):
+        raise ImportError("""
+    Importing %s disabled by IPython, which has
+    already imported an Incompatible QT Binding: %s
+    """ % (mod_name, loaded_api()))
+
+ID = ImportDenier()
+sys.meta_path.append(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')
+    else:
+        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', 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
+    return None
+
+
+def has_binding(api):
+    """Safely check for PyQt4 or PySide, without importing
+       submodules
+
+       Parameters
+       ----------
+       api : str [ 'pyqtv1' | 'pyqt' | 'pyside']
+            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'}
+    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__)
+
+        #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"""
+    current = loaded_api()
+    return has_binding(api) and current in [api, None]
+
+
+def import_pyqt4(version=2):
+    """
+    Import PyQt4
+
+    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
+    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
+
+    api = QT_API_PYQTv1 if version == 1 else QT_API_PYQT
+    return QtCore, QtGui, 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', and 'pyqtv1'
+
+    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_PYQTv1: partial(import_pyqt4, version=1)
+               }
+
+    for api in api_options:
+
+        if api not in loaders:
+            raise RuntimeError(
+                "Invalid Qt API %r, valid values are: %r, %r, %r" %
+                (api, QT_API_PYSIDE, QT_API_PYQT, QT_API_PYQTv1))
+
+        if not can_import(api):
+            continue
+
+        #cannot safely recover from an ImportError during this
+        result = loaders[api]()
+        commit_api(api)
+        return result
+    else:
+        raise ImportError("""
+    Could not load requested Qt binding. Please ensure that
+    PyQt4 >= 4.7 or PySide >= 1.0.3 is available,
+    and only one is imported per session.
+
+    Currently-imported Qt library:   %r
+    PyQt4 installed:                 %s
+    PySide >= 1.0.3 installed:       %s
+    Tried to load:                   %r
+    """ % (loaded_api(),
+           has_binding(QT_API_PYQT),
+           has_binding(QT_API_PYSIDE),
+           api_options))

IPython/external/qt.py

@@ -7,75 +7,17 b' Do not use this if you need PyQt with the old QString/QVariant API.'
 """
 
 import os
-from IPython.utils.version import check_version
-# Available APIs.
-QT_API_PYQT = 'pyqt'
-QT_API_PYSIDE = 'pyside'
 
-def prepare_pyqt4():
-    # For PySide compatibility, use the new-style string API that automatically
-    # converts QStrings to Unicode Python strings. Also, automatically unpack
-    # QVariants to their underlying objects.
-    import sip
-    sip.setapi('QString', 2)
-    sip.setapi('QVariant', 2)
+from IPython.external.qt_loaders import (load_qt, QT_API_PYSIDE,
+                                         QT_API_PYQT)
 
-# Select Qt binding, using the QT_API environment variable if available.
-QT_API = os.environ.get('QT_API')
+QT_API = os.environ.get('QT_API', None)
+if QT_API not in [QT_API_PYSIDE, QT_API_PYQT, None]:
+    raise RuntimeError("Invalid Qt API %r, valid values are: %r, %r" %
+                       (QT_API, QT_API_PYSIDE, QT_API_PYQT))
 if QT_API is None:
-    pyside_found = False
-    try:
-        import PySide
-        if not check_version(PySide.__version__, '1.0.3'):
-            # old PySide, fallback on PyQt
-            raise ImportError
-        # we can't import an incomplete pyside and pyqt4
-        # this will cause a crash in sip (#1431)
-        # check for complete presence before importing
-        import imp
-        imp.find_module("QtCore", PySide.__path__)
-        imp.find_module("QtGui", PySide.__path__)
-        imp.find_module("QtSvg", PySide.__path__)
-        pyside_found = True
-        from PySide import QtCore, QtGui, QtSvg
-        QT_API = QT_API_PYSIDE
-    except ImportError:
-        try:
-            prepare_pyqt4()
-            import PyQt4
-            from PyQt4 import QtCore, QtGui, QtSvg
-            if pyside_found:
-                print "WARNING: PySide installation incomplete and PyQt4 " \
-                      "present.\nThis will likely crash, please install " \
-                      "PySide completely, remove PySide or PyQt4 or set " \
-                      "the QT_API environment variable to pyqt or pyside"
-            if not check_version(QtCore.PYQT_VERSION_STR, '4.7'):
-                # PyQt 4.6 has issues with null strings returning as None
-                raise ImportError
-            QT_API = QT_API_PYQT
-        except ImportError:
-            raise ImportError('Cannot import PySide >= 1.0.3 or PyQt4 >= 4.7')
-
-elif QT_API == QT_API_PYQT:
-    # Note: This must be called *before* PyQt4 is imported.
-    prepare_pyqt4()
-
-# Now peform the imports.
-if QT_API == QT_API_PYQT:
-    from PyQt4 import QtCore, QtGui, 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
-
-elif QT_API == QT_API_PYSIDE:
-    import PySide
-    if not check_version(PySide.__version__, '1.0.3'):
-        raise ImportError("IPython requires PySide >= 1.0.3, found %s"%PySide.__version__)
-    from PySide import QtCore, QtGui, QtSvg
-
+    api_opts = [QT_API_PYSIDE, QT_API_PYQT]
 else:
-    raise RuntimeError('Invalid Qt API %r, valid values are: %r or %r' %
-                       (QT_API, QT_API_PYQT, QT_API_PYSIDE))
+    api_opts = [QT_API]
+
+QtCore, QtGui, QtSvg, QT_API = load_qt(api_opts)

IPython/external/qt_for_kernel.py

@@ -4,6 +4,9 b' This is the import used for the `gui=qt` or `pylab=qt` initialization.'
 
 Import Priority:
 
+if Qt4 has been imported anywhere else:
+   use that
+
 if matplotlib has been imported and doesn't support v2 (<= 1.0.1):
     use PyQt4 @v1
 
@@ -33,56 +36,49 b' import sys'
 
 from IPython.utils.warn import warn
 from IPython.utils.version import check_version
+from IPython.external.qt_loaders import (load_qt, QT_API_PYSIDE,
+                                         QT_API_PYQT, QT_API_PYQTv1,
+                                         loaded_api)
 
-matplotlib = sys.modules.get('matplotlib')
-if matplotlib and not check_version(matplotlib.__version__, '1.0.2'):
-    # 1.0.1 doesn't support pyside or v2, so stick with PyQt @v1,
-    # and ignore everything else
-    from PyQt4 import QtCore, QtGui
-else:
-    # ask QT_API ETS variable *first*
-    QT_API = os.environ.get('QT_API', None)
-    if QT_API is None:
-        # QT_API not set, ask matplotlib if it was imported (e.g. `pylab=qt`)
-        if matplotlib:
-            mpqt = matplotlib.rcParams.get('backend.qt4', None)
-        else:
-            mpqt = None
-        if mpqt is None:
-            # matplotlib not imported or had nothing to say.
-            try:
-                # default to unconfigured PyQt4
-                from PyQt4 import QtCore, QtGui
-            except ImportError:
-                # fallback on PySide
-                try:
-                    from PySide import QtCore, QtGui
-                except ImportError:
-                    raise ImportError('Cannot import PySide or PyQt4')
-        elif mpqt.lower() == 'pyqt4':
-            # import PyQt4 unconfigured
-            from PyQt4 import QtCore, QtGui
-        elif mpqt.lower() == 'pyside':
-            from PySide import QtCore, QtGui
-        else:
-            raise ImportError("unhandled value for backend.qt4 from matplotlib: %r"%mpqt)
-    else:
-        # QT_API specified, use PySide or PyQt+v2 API from external.qt
-        # this means ETS is likely to be used, which requires v2
-        try:
-            from IPython.external.qt import QtCore, QtGui
-        except ValueError as e:
-            if 'API' in str(e):
-                # PyQt4 already imported, and APIv2 couldn't be set
-                # Give more meaningful message, and warn instead of raising
-                warn("""
-    Assigning the ETS variable `QT_API=pyqt` implies PyQt's v2 API for
-    QString and QVariant, but PyQt has already been imported
-    with v1 APIs.  You should unset QT_API to work with PyQt4
-    in its default mode.
-""")
-                # allow it to still work
-                from PyQt4 import QtCore, QtGui
-            else:
-                raise
+#Constraints placed on an imported matplotlib
+def matplotlib_options(mpl):
+    if mpl is None:
+        return
+    mpqt = mpl.rcParams.get('backend.qt4', None)
+    if mpqt is None:
+        return None
+    if mpqt.lower() == 'pyside':
+        return [QT_API_PYSIDE]
+    elif mpqt.lower() == 'pyqt4':
+        return [QT_API_PYQTv1]
+    raise ImportError("unhandled value for backend.qt4 from matplotlib: %r" %
+                      mpqt)
+
+def get_options():
+    """Return a list of acceptable QT APIs, in decreasing order of
+    preference
+    """
+    #already imported Qt somewhere. Use that
+    loaded = loaded_api()
+    if loaded is not None:
+        return [loaded]
+
+    mpl = sys.modules.get('matplotlib', None)
+
+    if mpl is not None and check_version(mpl.__version__, '1.0.2'):
+        #1.0.1 only supports PyQt4 v1
+        return [QT_API_PYQTv1]
+
+    if os.environ.get('QT_API', None) is None:
+        #no ETS variable. Ask mpl, then use either
+        return matplotlib_options(mpl) or [QT_API_PYQTv1, QT_API_PYSIDE]
+
+    #ETS variable present. Will fallback to external.qt
+    return None
+
+api_opts = get_options()
+if api_opts is not None:
+    QtCore, QtGui, QtSvg, QT_API = load_qt(api_opts)
 
+else: # use ETS variable
+    from IPython.external.qt import QtCore, QtGui, QtSvg, QT_API