Kivy: How to correctly manipulate a widget in python that is defined in KV lang

Question

I have have the following that's written in KV lang:

    TextInput:
        id: user_input_temp
        font_size: 50
        size_hint_y: None
        input_filter: 'float'
        multiline: False

    Label:
        text: "Celsius"
    Label:
        id: celsius
        text: root.temp_conv()

And I attempt to use user_input_temp in python code:

    class Temperature(Screen,BoxLayout):

        def temp_conv(self):
            number = self.ids.user_input_temp.text
            input =  float(number)
            celsius = (input - 32)*(5/9)
            self.ids.celsius.text = str(celsius)

But I receive an error - ValueError: could not convert string to float: How can I correctly convert .text of the widget? (preferably by using the widget id)

Answer 1

Check what value it can't convert. In your example, you don't actually set the text so it's probably doing float('') , which would give the error that you see since '' doesn't describe a float. In that case you'd want to try to do the conversion, but return something suitable or do nothing at all if it fails.