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Kivy introduces a new way of declaring properties within a class. Before:

class MyClass(object):
    def __init__(self):
        super(MyClass, self).__init__()
        self.numeric_var = 1

After, using Kivy’s properties:

class MyClass(EventDispatcher):
    numeric_var = NumericProperty(1)

These properties implement the Observer pattern. They help you to:

  • Easily manipulate widgets defined in the Kv language

  • Automatically observe any changes and dispatch functions/code accordingly

  • Check and validate values

  • Optimize memory management

To use them, you have to declare them at class level. That is, directly in the class, not in any method of the class. A property is a class attribute that will automatically create instance attributes. Each property by default provides an on_<propertyname> event that is called whenever the property’s state/value changes.

Kivy provides the following properties:

NumericProperty, StringProperty, ListProperty, ObjectProperty, BooleanProperty, BoundedNumericProperty, OptionProperty, ReferenceListProperty, AliasProperty, DictProperty, VariableListProperty, ConfigParserProperty, ColorProperty

For an in-depth explanation, take a look at Properties.