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