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

i have have 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 attempt 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 receive error - valueerror: not convert string float: how can correctly convert .text of widget? (preferably using widget id)

check value can't convert. in example, don't set text it's doing float(''), give error see since '' doesn't describe float. in case you'd want try conversion, return suitable or nothing @ if fails.