title: How can I get widget's/layout's actual size in Kivy?
body: <p>I have this layout inside BoxLayout (along with another elements):</p>
  
  <pre><code>&lt;PlayField&gt;:
      size_hint_x: None
      width: self.height
      canvas.before:
          Color:
              rgb: .9, .9, .9
          Rectangle:
              pos: self.pos
              size: self.size
  </code></pre>
  
  <p>main.py:</p>
  
  <pre><code>class PlayField(Layout):  # Or should it be Widget?
      pass
  </code></pre>
  
  <p>How do I get actual size of it? <code>print(self.size)</code> shows default size (100, 100), although it's not true.</p>