""" Defines miscellaneous Qt-related helper classes and functions.
"""
import inspect
from qtpy import QtCore, QtGui
from ipython_genutils.py3compat import iteritems
from traitlets import HasTraits, TraitType
#-----------------------------------------------------------------------------
# Metaclasses
#-----------------------------------------------------------------------------
MetaHasTraits = type(HasTraits)
MetaQObject = type(QtCore.QObject)
class MetaQObjectHasTraits(MetaQObject, MetaHasTraits):
""" A metaclass that inherits from the metaclasses of HasTraits and QObject.
Using this metaclass allows a class to inherit from both HasTraits and
QObject. Using SuperQObject instead of QObject is highly recommended. See
QtKernelManager for an example.
"""
def __new__(mcls, name, bases, classdict):
# FIXME: this duplicates the code from MetaHasTraits.
# I don't think a super() call will help me here.
for k,v in iteritems(classdict):
if isinstance(v, TraitType):
v.name = k
elif inspect.isclass(v):
if issubclass(v, TraitType):
vinst = v()
vinst.name = k
classdict[k] = vinst
cls = MetaQObject.__new__(mcls, name, bases, classdict)
return cls
def __init__(mcls, name, bases, classdict):
# Note: super() did not work, so we explicitly call these.
MetaQObject.__init__(mcls, name, bases, classdict)
MetaHasTraits.__init__(mcls, name, bases, classdict)
#-----------------------------------------------------------------------------
# Classes
#-----------------------------------------------------------------------------
def superQ(QClass):
""" Permits the use of super() in class hierarchies that contain Qt classes.
Unlike QObject, SuperQObject does not accept a QObject parent. If it did,
super could not be emulated properly (all other classes in the heierarchy
would have to accept the parent argument--they don't, of course, because
they don't inherit QObject.)
This class is primarily useful for attaching signals to existing non-Qt
classes. See QtKernelManagerMixin for an example.
"""
class SuperQClass(QClass):
def __new__(cls, *args, **kw):
# We initialize QClass as early as possible. Without this, Qt complains
# if SuperQClass is not the first class in the super class list.
inst = QClass.__new__(cls)
QClass.__init__(inst)
return inst
def __init__(self, *args, **kw):
# Emulate super by calling the next method in the MRO, if there is one.
mro = self.__class__.mro()
for qt_class in QClass.mro():
mro.remove(qt_class)
next_index = mro.index(SuperQClass) + 1
if next_index < len(mro):
mro[next_index].__init__(self, *args, **kw)
return SuperQClass
SuperQObject = superQ(QtCore.QObject)
#-----------------------------------------------------------------------------
# Functions
#-----------------------------------------------------------------------------
def get_font(family, fallback=None):
"""Return a font of the requested family, using fallback as alternative.
If a fallback is provided, it is used in case the requested family isn't
found. If no fallback is given, no alternative is chosen and Qt's internal
algorithms may automatically choose a fallback font.
Parameters
----------
family : str
A font name.
fallback : str
A font name.
Returns
-------
font : QFont object
"""
font = QtGui.QFont(family)
# Check whether we got what we wanted using QFontInfo, since exactMatch()
# is overly strict and returns false in too many cases.
font_info = QtGui.QFontInfo(font)
if fallback is not None and font_info.family() != family:
font = QtGui.QFont(fallback)
return font
