Change canvas size from .py on kiy

Question

I am trying to change the canvas size of an image randomly. I have 10 images in a GridLayout and I want to randomly resize one of them. I have tried several ways but I can't figure it out, what am I doing wrong?

.kv

<ButOpcion>:
    canvas.before:
        Rectangle:
            pos: self.pos
            size: 250, 250
            source: "data/img/letra_d/dragon.png"
   

<ContainerCaza>:
    canvas.before:
        Rectangle:
            pos: self.pos
            size: self.size
            source: 'data/img/fondobosque.jpg'
           
    but_1: but1
    but_2: but2
    but_3: but3
    but_4: but4
    but_5: but5
    but_6: but6
    but_7: but7
    but_8: but8
    but_9: but9
    but_10: but10
    
    BoxLayout:
        orientation: 'vertical'
        Label:
            text: 'Ahora debes localizar al intruso entre estas imágenes. ¡Fíjate bien, una de las imágenes es distinta!'
            size_hint_y: None
            text_size: self.width, None
            #height: self.texture_size[1]
            halign: 'center'
            valign: 'middle'
            padding: (20,15)
            font_size: 25
            color: (.66, .38, .14, 1)
        
        GridLayout:
            pos_hint: {"center_x": 0.5, "center_y": 0.5}
            cols: 5
            spacing: '10dp'
            #size_hint: 0.6, 0.6
            
            ButOpcion:
                id: but1
                
            ButOpcion:
                id: but2
                  
            ButOpcion:
                id: but3
                 
            ButOpcion:
                id: but4
               
            ButOpcion:
                id: but5
                
            ButOpcion:
                id: but6
                
            ButOpcion:
                id: but7
                
            ButOpcion:
                id: but8
                
            ButOpcion:
                id: but9
                
            ButOpcion:
                id: but10
                        
        Button:
            size_hint:.06, 0.1
            text: "Volver al menú"
            on_release: app.root.current = 'menu'

.py

__all__ = ('Caza')

import kivy
kivy.require('1.0.6')

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.widget import Widget
from kivy.uix.gridlayout import GridLayout
from random import choice, random
from kivy.properties import ObjectProperty
from kivy.graphics import Rectangle

#Builder.load_file('caza.kv')

class ButOpcion(Widget):
    pass

class ContainerCaza(Screen):
    def __init__(self, **kwargs):
        super(ContainerCaza, self).__init__(**kwargs)
    
    def intruso(self):
        but_1 = ObjectProperty(None)
        but_2 = ObjectProperty(None)
        but_3 = ObjectProperty(None)
        but_4 = ObjectProperty(None)
        but_5 = ObjectProperty(None)
        but_6 = ObjectProperty(None)
        but_7 = ObjectProperty(None)
        but_8 = ObjectProperty(None)
        but_9 = ObjectProperty(None)
        but_10 = ObjectProperty(None)
        
        target = choice(['but1', 'but2', 'but3', 'but4', 'but5', 'but6', 'but7', 'but8', 'but9', 'but10'])
        print(target)
        
        if target == 'but1':
            def ChangeImage1(self):
                self.ids.but1.size = 10, 10
        elif target == 'but2':
            def ChangeImage2(self):
                self.ids.but2.size = 10, 10
        elif target == 'but3':
            def ChangeImage3(self):
                self.ids.but3.size = 10, 10
        elif target == 'but4':
            def ChangeImage4(self):
                self.ids.but4.size = 10, 10
        elif target == 'but5':
            def ChangeImage5(self):
                self.ids.but5.size = 10, 10
        elif target == 'but6':
            def ChangeImage6(self):
                self.ids.but6.size = 10, 10
        elif target == 'but7':
            def ChangeImage7(self):
                self.ids.but7.size = 10, 10
        elif target == 'but8':
            def ChangeImage8(self):
                self.ids.but8.size = 10, 10
        elif target == 'but9':
            def ChangeImage9(self):
                self.ids.but9.size = 10, 10
        else:
            def ChangeImage10(self):
                self.ids.but10.size = 10, 10
        
class CazaApp(App):
    def build(self):
        #Window.fullscreen = 'auto'
        caza = ContainerCaza()
        caza.intruso()
        return caza
    
if __name__ == "__main__":
    CazaApp().run()

How can I access the canvas.before from the .py file? I'm new to python and kivy and I'm a bit lost, there are a lot of things I don't know how to do.

Answer 1

Thanks John, it seems to work correctly now, but aesthetically, it places the GridLayout in the upper left corner.

Answer 2

In your intruso() method, you are defining inner methods that can change the size of a ButOpcion, but you never call those inner methods. I don't see any purpose to creating an inner method here, so I think you should just execute the code that you are putting in the inner method:

def intruso(self, *args):

    target = choice(['but1', 'but2', 'but3', 'but4', 'but5', 'but6', 'but7', 'but8', 'but9', 'but10'])
    print(target)

    if target == 'but1':
        self.ids.but1.size = 10, 10
    elif target == 'but2':
        self.ids.but2.size = 10, 10
    .
    .
    .

And rather than trying to change the size of the canvas directly, just change the size of the ButOpcion and let the canvas adjust to it. This can be done by defining your ButOpcion in the kv as:

<ButOpcion>:
    size_hint: None, None
    size: 250, 250
    canvas.before:
        Rectangle:
            pos: self.pos
            size: self.size
            source: "data/img/letra_d/dragon.png"