IPython/external/qt_for_kernel.py

""" Import Qt in a manner suitable for an IPython kernel.

This is the import used for the `gui=qt` or `matplotlib=qt` initialization.

Import Priority:

if Qt has been imported anywhere else:
   use that

if matplotlib has been imported and doesn't support v2 (<= 1.0.1):
    use PyQt4 @v1

Next, ask QT_API env variable

if QT_API not set:
    ask matplotlib via rcParams['backend.qt4']
    if it said PyQt:
        use PyQt4 @v1
    elif it said PySide:
        use PySide

    else: (matplotlib said nothing)
        # this is the default path - nobody told us anything
        try:
            PyQt @v1
        except:
            fallback on PySide
else:
    use what QT_API says

"""
# NOTE: This is no longer an external, third-party module, and should be
# considered part of IPython. For compatibility however, it is being kept in
# IPython/external.

import os
import sys

from IPython.utils.version import check_version
from IPython.external.qt_loaders import (load_qt, loaded_api, QT_API_PYSIDE,
                                         QT_API_PYQT, QT_API_PYQT5,
                                         QT_API_PYQTv1, QT_API_PYQT_DEFAULT)

_qt_apis = (QT_API_PYSIDE, QT_API_PYQT, QT_API_PYQT5, QT_API_PYQTv1,
            QT_API_PYQT_DEFAULT)

#Constraints placed on an imported matplotlib
# TODO: Make sure this logic is still in sync with matplotlib's requirements.
# In particular, matplotlib can also now support a qt5 backend, and so this will
# break if matplotlib is imported and running happily with qt5, because
# it only queries for the preferred qt4 option.
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_PYQT_DEFAULT]
    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 not check_version(mpl.__version__, '1.0.2'):
        #1.0.1 only supports PyQt4 v1
        return [QT_API_PYQT_DEFAULT]

    qt_api = os.environ.get('QT_API', None)
    if qt_api is None:
        #no ETS variable. Ask mpl, then use either
        return matplotlib_options(mpl) or [QT_API_PYQT_DEFAULT, QT_API_PYSIDE]
    elif qt_api not in _qt_apis:
        raise RuntimeError("Invalid Qt API %r, valid values are: %r" %
                           (qt_api, ', '.join(_qt_apis)))
    else:
        return [qt_api]

api_opts = get_options()
QtCore, QtGui, QtSvg, QT_API = load_qt(api_opts)