Support for QSettings

Qt provies the QSettings class as a platform independent API for the persistent storage and retrieval of application settings. Settings are retrieved using the value() method. However the type of the value returned may not be what is expected. Some platforms only ever store string values which means that the type of the original value is lost. Therefore a setting with an integer value of 42 may be retrieved (on some platforms) as a string value of '42'.

As a solution to this problem PyQt5’s implementation of value() takes an optional third argument called type. This is either a Python type object, e.g. int, or a string that is the name of a C++ type, e.g. 'QStringList'. The value returned will be an object of the requested type.

For example:

from PyQt5.QtCore import QSettings, QPoint

settings = QSettings('foo', 'foo')

settings.setValue('int_value', 42)
settings.setValue('point_value', QPoint(10, 12))

# This will write the setting to the platform specific storage.
del settings

settings = QSettings('foo', 'foo')

int_value = settings.value('int_value', type=int)
print("int_value: %s" % repr(int_value))

point_value = settings.value('point_value', type=QPoint)
print("point_value: %s" % repr(point_value))

When this is executed then the following will be displayed for all platforms:

int_value: 42
point_value: PyQt5.QtCore.QPoint(10, 20)

If the value of the setting is a container (corresponding to either QVariantList, QVariantMap or QVariantHash) then the type is applied to the contents of the container.

For example:

from PyQt5.QtCore import QSettings

settings = QSettings('foo', 'foo')

settings.setValue('list_value', [1, 2, 3])
settings.setValue('dict_value', {'one': 1, 'two': 2})

# This will write the setting to the platform specific storage.
del settings

settings = QSettings('foo', 'foo')

list_value = settings.value('list_value', type=int)
print("list_value: %s" % repr(list_value))

dict_value = settings.value('dict_value', type=int)
print("dict_value: %s" % repr(dict_value))

When this is executed then the following will be displayed for all platforms:

list_value: [1, 2, 3]
dict_value: {'one': 1, 'two': 2}