Kivy ProgressBar-value doesn't get updated when kwargs' position switched.

[ApuCoder]

I'm using Kivy (v-2.0.0) [Python (v-3.9.7)].

The problem I noticed the unexpected behaviour (behavior) when initialized the ProgressBar with the attrs. max and value with different order such as ProgressBar(max = 1000, value = 450) or ProgressBar(value = 450, max = 1000). They both render different result.

What I tried but didn't work I tried to bind the attr. "max" with the AliasProperty value, setting different cache values, but none of them seem to work for me. I think (not quite sure) this problem arises due to the setter method.

What seems to work I changed the attr. value to BoundedNumericProperty as BoundedNumericProperty(0.0, min = 0, errorvalue = 0) and redefine it in the init as

    def __init__(self, **kwargs):
        #self._value = 0.
        super(ProgressBar, self).__init__(**kwargs)
        self.value = min(self.max, self.value) # To limit the upper-value of the attr: value within attr: max.

Now I got the result in both cases as expected.

Executable (for the original problem)

from kivy.app import runTouchApp
from kivy.uix.progressbar import ProgressBar

pb = ProgressBar(max = 1000, value = 450) # This works as intended.
#pb = ProgressBar(value = 450, max = 1000) # This does not work as intended.
print(f"{pb.max = }, {pb.value = }")

runTouchApp(pb)

[ApuCoder]

Well, I noticed again this doesn't solve the issue completely, as the attr. value can be (made) unbounded above at runtime.

[kuzeyron]

Looks to me like you are calling the super() in the wrong class. You should be seeing something in the logs about this.

[ApuCoder]

No, actually I did it in source code of ProgressBar after observing that odd behaviour. Did you also notice that same behaviour after altering the position of kwargs ?

[kuzeyron]

No, actually I did it in source code of ProgressBar after observing that odd behaviour. Did you also notice that same behaviour after altering the position of kwargs ?

Not the best practice on editing the source code of Kivy. Here is one example that works:

from kivy.app import App
from kivy.properties import NumericProperty
from kivy.uix.progressbar import ProgressBar


class MyProgressBar(ProgressBar):
    max = NumericProperty(20)
    value = NumericProperty(50)
    default = NumericProperty(1)

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.value = min(self.max, self.value) if self.value <= self.max else self.default


class ProgressBarTest(App):

    def build(self):

        return MyProgressBar()


if __name__ == '__main__':
    ProgressBarTest().run()

[ApuCoder]

It looks like I failed to describe the problem properly. I ran the above code (Executable (for the original problem)) as described in the source code of ProgressBar. But when change the kwargs (as above) I noticed that behaviour.

[kuzeyron]

Not a problem on my end:

from kivy.app import App
from kivy.properties import NumericProperty
from kivy.uix.progressbar import ProgressBar


class MyProgressBar(ProgressBar):
    max = NumericProperty(20)
    value = NumericProperty(50)
    default = NumericProperty(1)

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.value = min(self.max, self.value) if self.value <= self.max else self.default


class ProgressBarTest(App):

    def build(self):

        return MyProgressBar(value=20, max=50)


if __name__ == '__main__':
    ProgressBarTest().run()

Now try changing the direction. If there are other variables/functions you need from ProgressBar you just add them in there. Or write it like this:

from kivy.app import App
from kivy.properties import NumericProperty
from kivy.uix.progressbar import ProgressBar


class MyProgressBar(ProgressBar):
    max = NumericProperty(20)
    value = NumericProperty(50)
    default = NumericProperty(1)

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.value = min(self.max, self.value) if self.value <= self.max else self.default


class ProgressBarTest(App):

    def build(self):
        root = MyProgressBar()
        root.value = 20
        root.max = 70

        return root


if __name__ == '__main__':
    ProgressBarTest().run()

[ApuCoder]

Alas ! Yet again I failed to describe the problem,

Ok, when I run,

from kivy.app import runTouchApp
from kivy.uix.progressbar import ProgressBar

pb = ProgressBar(max = 1000, value = 450) # This works as intended.
print(f"{pb.max = }, {pb.value = }")

runTouchApp(pb)

I got, pb.max = 1000, pb.value = 450.

But when I did,

from kivy.app import runTouchApp
from kivy.uix.progressbar import ProgressBar

pb = ProgressBar(value = 450, max = 1000) # This does not work as intended.
print(f"{pb.max = }, {pb.value = }")

runTouchApp(pb)

I got, pb.max = 1000, pb.value = 100.0

Please, just let me know if this is an error from my side or really a bug.

[kuzeyron]

Thank you! Now I understand the problem. I will look into the source code. But for now you can use:

from kivy.app import runTouchApp
from kivy.uix.progressbar import ProgressBar
from kivy.properties import NumericProperty

class MyProg(ProgressBar):
    value = NumericProperty(0)


if __name__ == '__main__':
    pb = MyProg(value=450, max=1000) # This does not work as intended.
    print(f"{pb.max = }, {pb.value = }")

    runTouchApp(pb)

[ApuCoder]

Yes that's why I tried changing AliasProperty by BoundedNumericProperty.

[kuzeyron]

As I had a conversation on Discord with the Core-Devs. They suggested updating the documentation page and being specific about what you said about placing the arguments in the right order.

[ApuCoder]

I will argue that value should be allowed to be modified by user i.e. it should be a NumericProperty (or at least BoundedNumericProperty with min = 0 maybe) instead of the current AliasProperty.

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