How to get a boolean value from QSettings correctly?

NonNT

How to get a boolean value from QSettings correctly without helper function?

Value is 'str' if setting key is defined
Value is 'bool' if default value is True
Value is 'NoneType' if default value is False

def readSettings(self):
    settings = QSettings()
    showTitle = self.valueToBool(settings.value('Settings/showTitle', True))

def valueToBool(self, value):
    if type(value) is str:
        return True if value == 'true' else False
    elif value is None:
        return False
    else:
        return value

Pyside2 5.13.1 on Manjaro

JonB

@NonNT
I thought about this for a while! I claim there is not a perfect solution to your case which obeys your rules, is an in-liner (short, and using only Python in-builts), does not raise an exception, does not use regular expressions and does not evaluate the expression more than once. :)

The best I can come up with which obeys these is:

str(expr) in ['true', '1']

Obviously this means that only entries of true or 1 are true, everything else (including None, the empty string ('') and e.g. 0 or 2 or 1.0). You could also accept True or TRUE with str(expr).lower() ....

Having said that, most people would write a function, and that allows us to reference the value parameter more than once. The shortest I would offer is:

@staticmethod
def valueToBool(value):
    return value.lower() == 'true' if isinstance(value, str) else bool(value)

This treats, say, 2 or 1.0 as true rather than false, unlike the in-liner. Which behaviour you prefer for such a case is probably a matter of taste!

A lot of Pythonistas would write the function multi-line to use int(value) inside a try ... except .... Personally I don't like multi-lines where one would suffice and I just don't like raising exceptions in the way they are fond of, but that's up to you. In any case this would be the opposite of what you are asking for.

NonNT

@JonB
It looks great. Thanks

def writeSettings(self):
    showTitle = self.showTitleCheckBox.isChecked()
    settings = QSettings()
    settings.setValue('Settings/showTitle', showTitle)

def readSettings(self):
    settings = QSettings()
    showTitle = self.valueToBool(settings.value('Settings/showTitle', True))
    self.showTitleCheckBox.setChecked(showTitle)

@staticmethod
def valueToBool(value):
    return value.lower() == 'true' if isinstance(value, str) else bool(value)

Pablo J. Rogina

@NonNT said in How to get a boolean value from QSettings correctly?:

It looks great.

time to mark your post as solved then? Thanks.

V__V

PyQt provides an extra type argument to fix such a problem:

r = settings.value("Settings/showTitle", True, type=bool)
print(r, type(r))
False <class 'bool'>

Here i use PyQt 5.9.2

StarChild

settings.setValue('Settings/showTitle', int(False))

settings.value('Settings/showTitle', True)

strawbotics

To make sure results are consistent and repeatable clear the settings before setting them.

settings.clear()
settings.setValue("Settings/showTitle", False)
print(settings.value("Settings/showTitle", type=bool)

This solution works on macOS and Windows.

The other thing to be careful about when working cross platform is always use the same case for keys and never use case to differentiate two keys. Windows init file is case insensitive while macOS is case sensitive.

friedemannkleint

PySide also let's you specify a type:

https://doc.qt.io/qtforpython-6/PySide6/QtCore/QSettings.html#PySide6.QtCore.PySide6.QtCore.QSettings.value