Kivy: Manipulating dynamically created widgets in update function - python-3.x

Question

I am trying to extend the code in the answer here provided by Nykakin where widgets are defined on the fly in Kivy, dynamically assigned IDs, and then manipulated based on ID.
The 'end game' is to implement some basic 2D physics by changing position of widgets based on ID.
I am not able to 'walk' the widget tree from the update function (errors inline).
Is it possible to do such a thing?
Here is the code:
#code begins here
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.stacklayout import StackLayout
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.clock import Clock
from kivy.factory import Factory
class MyWidget(BoxLayout):
def __init__(self, **kwargs):
super().__init__(**kwargs)
button = Button(text="Print IDs", id="PrintIDsButton")
button.bind(on_release=self.print_label)
self.add_widget(button)
# crate some labels with defined IDs
for i in range(5):
self.add_widget(Button(text=str(i), id="button no: " + str(i)))
# update moved as per inclement's recommendation
Clock.schedule_interval(MyApp.update, 1 / 30.0)
def print_label(self, *args):
children = self.children[:]
while children:
child = children.pop()
print("{} -> {}".format(child, child.id))
# we can change label properties from here! Woo!
children.extend(child.children)
if child.id == "PrintIDsButton":
child.text = child.text + " :)"
class MyApp(App):
def build(self):
return MyWidget()
def update(self, *args):
#ERROR# AttributeError: 'float' object has no attribute 'root'
children = self.root.children[:]
#ERROR# TypeError: 'kivy.properties.ListProperty' object is not subscriptable
#children = MyWidget.children[:]
#while children:
# child = children.pop()
# print("{} -> {}".format(child, child.id))
# children.extend(child.children)
#ERROR# TypeError: 'kivy.properties.ListProperty' object is not iterable
#for child in MyWidget.children:
# print("{} -> {}".format(child, child.id))
if __name__ == '__main__':
MyApp().run()
Windows 7 SP1
Kivy 1.8.0 / Python 3.3
My apologies if my terminology is incorrect! (and thank you for your time)

Answer 1

children = MyWidget.children[:]
MyWidget is the class itself, not an instance of it, and so the children is a ListProperty object and not the actual list you want.
You want instead the children of the MyWidget instance that is your root widget, self.root.children.
Also, you clock schedule the update function at class level; I think this is bad practice, and could lead to subtle bugs. It would be more normal to do it in the __init__ method of the widget instead.

Answer 2

So putting the update function within the 'MyWidget' class and then accessing elements within 'MyWidget' by calling self.children worked!
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.stacklayout import StackLayout
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.clock import Clock
from kivy.factory import Factory
class MyWidget(BoxLayout):
def __init__(self, **kwargs):
super().__init__(**kwargs)
button = Button(text="Print IDs", id="PrintIDsButton")
button.bind(on_release=self.print_label)
self.add_widget(button)
# crate some labels with defined IDs
for i in range(5):
self.add_widget(Button(text=str(i), id="button no: " + str(i)))
# update moved as per inclement's recommendation
Clock.schedule_interval(self.update, 1 / 5.0)
def print_label(self, *args):
children = self.children[:]
while children:
child = children.pop()
print("{} -> {}".format(child, child.id))
# Add smiley by ID
children.extend(child.children)
if child.id == "PrintIDsButton":
child.text = child.text + " :)"
def update(self, *args):
children = self.children[:]
while children:
child = children.pop()
# remove smiley by ID
if child.id == "PrintIDsButton":
child.text = "Print IDs"
class MyApp(App):
def build(self):
return MyWidget()
if __name__ == '__main__':
MyApp().run()
Thanks again to inclement!