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Kivy Namespaces

New in version 1.9.1.


This code is still experimental, and its API is subject to change in a future version.

The KNSpaceBehavior mixin class provides namespace functionality for Kivy objects. It allows kivy objects to be named and then accessed using namespaces.

KNSpace instances are the namespaces that store the named objects in Kivy ObjectProperty instances. In addition, when inheriting from KNSpaceBehavior, if the derived object is named, the name will automatically be added to the associated namespace and will point to a proxy_ref of the derived object.

Basic examples

By default, there’s only a single namespace: the knspace namespace. The simplest example is adding a widget to the namespace:

from kivy.uix.behaviors.knspace import knspace
widget = Widget()
knspace.my_widget = widget

This adds a kivy ObjectProperty with rebind=True and allownone=True to the knspace namespace with a property name my_widget. And the property now also points to this widget.

This can be done automatically with:

class MyWidget(KNSpaceBehavior, Widget):

widget = MyWidget(knsname='my_widget')

Or in kv:


    knsname: 'my_widget'

Now, knspace.my_widget will point to that widget.

When one creates a second widget with the same name, the namespace will also change to point to the new widget. E.g.:

widget = MyWidget(knsname='my_widget')
# knspace.my_widget now points to widget
widget2 = MyWidget(knsname='my_widget')
# knspace.my_widget now points to widget2

Setting the namespace

One can also create ones own namespace rather than using the default knspace by directly setting KNSpaceBehavior.knspace:

class MyWidget(KNSpaceBehavior, Widget):

widget = MyWidget(knsname='my_widget')
my_new_namespace = KNSpace()
widget.knspace = my_new_namespace

Initially, my_widget is added to the default namespace, but when the widget’s namespace is changed to my_new_namespace, the reference to my_widget is moved to that namespace. We could have also of course first set the namespace to my_new_namespace and then have named the widget my_widget, thereby avoiding the initial assignment to the default namespace.

Similarly, in kv:


    knspace: KNSpace()
    knsname: 'my_widget'

Inheriting the namespace

In the previous example, we directly set the namespace we wished to use. In the following example, we inherit it from the parent, so we only have to set it once:


    knsname: 'my_complex'
        knsname: 'label1'
        knsname: 'label2'

Then, we do:

widget = MyComplexWidget()
new_knspace = KNSpace()
widget.knspace = new_knspace

The rule is that if no knspace has been assigned to a widget, it looks for a namespace in its parent and parent’s parent and so on until it find one to use. If none are found, it uses the default knspace.

When MyComplexWidget is created, it still used the default namespace. However, when we assigned the root widget its new namespace, all its children switched to using that new namespace as well. So new_knspace now contains label1 and label2 as well as my_complex.

If we had first done:

widget = MyComplexWidget()
new_knspace = KNSpace()
knspace.label1.knspace = knspace
widget.knspace = new_knspace

Then label1 would remain stored in the default knspace since it was directly set, but label2 and my_complex would still be added to the new namespace.

One can customize the attribute used to search the parent tree by changing KNSpaceBehavior.knspace_key. If the desired knspace is not reachable through a widgets parent tree, e.g. in a popup that is not a widget’s child, KNSpaceBehavior.knspace_key can be used to establish a different search order.

Accessing the namespace

As seen in the previous example, if not directly assigned, the namespace is found by searching the parent tree. Consequently, if a namespace was assigned further up the parent tree, all its children and below could access that namespace through their KNSpaceBehavior.knspace property.

This allows the creation of multiple widgets with identically given names if each root widget instance is assigned a new namespace. For example:

        text: root.knspace.pretty.text if root.knspace.pretty else ''

    knsname: 'pretty'
    text: 'Hello'


Now, when we do:

knspace1, knspace2 = KNSpace(), KNSpace()
composite1 = MyCompositeWidget()
composite1.knspace = knspace1

composite2 = MyCompositeWidget()
composite2.knspace = knspace2

knspace1.pretty = "Here's the ladder, now fix the roof!"
knspace2.pretty = "Get that raccoon off me!"

Because each of the MyCompositeWidget instances have a different namespace their children also use different namespaces. Consequently, the pretty and complex widgets of each instance will have different text.

Further, because both the namespace ObjectProperty references, and KNSpaceBehavior.knspace have rebind=True, the text of the MyComplexWidget label is rebound to match the text of MyPrettyWidget when either the root’s namespace changes or when the root.knspace.pretty property changes, as expected.

Forking a namespace

Forking a namespace provides the opportunity to create a new namespace from a parent namespace so that the forked namespace will contain everything in the origin namespace, but the origin namespace will not have access to anything added to the forked namespace.

For example:

child = knspace.fork()
grandchild = child.fork()

child.label = Label()
grandchild.button = Button()

Now label is accessible by both child and grandchild, but not by knspace. And button is only accessible by the grandchild but not by the child or by knspace. Finally, doing grandchild.label = Label() will leave grandchild.label and child.label pointing to different labels.

A motivating example is the example from above:

        text: root.knspace.pretty.text if root.knspace.pretty else ''

    knsname: 'pretty'
    text: 'Hello'

    knspace: 'fork'

Notice the addition of knspace: ‘fork’. This is identical to doing knspace: self.knspace.fork(). However, doing that would lead to infinite recursion as that kv rule would be executed recursively because self.knspace will keep on changing. However, allowing knspace: ‘fork’ cirumvents that. See KNSpaceBehavior.knspace.

Now, having forked, we just need to do:

composite1 = MyCompositeWidget()
composite2 = MyCompositeWidget()

composite1.knspace.pretty = "Here's the ladder, now fix the roof!"
composite2.knspace.pretty = "Get that raccoon off me!"

Since by forking we automatically created a unique namespace for each MyCompositeWidget instance.

class kivy.uix.behaviors.knspace.KNSpace(parent=None, keep_ref=False, **kwargs)[source]

Bases: kivy.event.EventDispatcher

Each KNSpace instance is a namespace that stores the named Kivy objects associated with this namespace. Each named object is stored as the value of a Kivy ObjectProperty of this instance whose property name is the object’s given name. Both rebind and allownone are set to True for the property.

See KNSpaceBehavior.knspace for details on how a namespace is associated with a named object.

When storing an object in the namespace, the object’s proxy_ref is stored if the object has such an attribute.

parent: (internal) A KNSpace instance or None.

If specified, it’s a parent namespace, in which case, the current namespace will have in its namespace all its named objects as well as the named objects of its parent and parent’s parent etc. See fork() for more details.


Returns a new KNSpace instance which will have access to all the named objects in the current namespace but will also have a namespace of its own that is unique to it.

For example:

forked_knspace1 = knspace.fork()
forked_knspace2 = knspace.fork()

Now, any names added to knspace will be accessible by the forked_knspace1 and forked_knspace2 namespaces by the normal means. However, any names added to forked_knspace1 will not be accessible from knspace or forked_knspace2. Similar for forked_knspace2.

keep_ref = False

Whether a direct reference should be kept to the stored objects. If True, we use the direct object, otherwise we use proxy_ref when present.

Defaults to False.

parent = None

(internal) The parent namespace instance, KNSpace, or None. See fork().

property(name, quiet=False)[source]

Get a property instance from the property name. If quiet is True, None is returned instead of raising an exception when name is not a property. Defaults to False.

New in version 1.0.9.

Returns:A Property derived instance corresponding to the name.

Changed in version 1.9.0: quiet was added.

class kivy.uix.behaviors.knspace.KNSpaceBehavior(knspace=None, **kwargs)[source]

Bases: builtins.object

Inheriting from this class allows naming of the inherited objects, which are then added to the associated namespace knspace and accessible through it.

Please see the knspace behaviors module documentation for more information.


The name given to this instance. If named, the name will be added to the associated knspace namespace, which will then point to the proxy_ref of this instance.

When named, one can access this object by e.g. self.knspace.name, where name is the given name of this instance. See knspace and the module description for more details.


The namespace instance, KNSpace, associated with this widget. The knspace namespace stores this widget when naming this widget with knsname.

If the namespace has been set with a KNSpace instance, e.g. with self.knspace = KNSpace(), then that instance is returned (setting with None doesn’t count). Otherwise, if knspace_key is not None, we look for a namespace to use in the object that is stored in the property named knspace_key, of this instance. I.e. object = getattr(self, self.knspace_key).

If that object has a knspace property, then we return its value. Otherwise, we go further up, e.g. with getattr(object, self.knspace_key) and look for it’s knspace property.

Finally, if we reach a value of None, or knspace_key was None, the default knspace namespace is returned.

If knspace is set to the string ‘fork’, the current namespace in knspace will be forked with KNSpace.fork() and the resulting namespace will be assigned to this instance’s knspace. See the module examples for a motivating example.

Both rebind and allownone are True.


The name of the property of this instance, to use to search upwards for a namespace to use by this instance. Defaults to ‘parent’ so that we’ll search the parent tree. See knspace.

When None, we won’t search the parent tree for the namespace. allownone is True.

kivy.uix.behaviors.knspace.knspace = <kivy.uix.behaviors.knspace.KNSpace object>

The default KNSpace namespace. See KNSpaceBehavior.knspace for more details.