PinchLabel to StackLayout

relevant.kv

  StackLayout:
      PinchLabel:
          text: 'hello'

relevant.py

import kivy
kivy.require('1.9.0')
 
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.label import Label
from kivy.vector import Vector
from kivy.properties import BoundedNumericProperty
 
class PinchLabel(Label):
    font_size_min = BoundedNumericProperty(2, min=0)
    font_size_max = BoundedNumericProperty(1e100, min=0)
 
    def __init__(self, **kwargs):
        super(PinchLabel, self).__init__(**kwargs)
        self._touches = []
        self._last_touch_pos = {}
 
    def on_touch_down(self, touch):
        if not self.collide_point(*touch.pos):
            return
 
        if 'multitouch_sim' in touch.profile:
            touch.multitouch_sim = True
 
        touch.grab(self)
        self._touches.append(touch)
        self._last_touch_pos[touch] = touch.pos
        return True
 
    def on_touch_move(self, touch):
        if touch in self._touches and touch.grab_current == self:
            self.scale_with_touch(touch)
            self._last_touch_pos[touch] = touch.pos
 
        if self.collide_point(*touch.pos):
            return True
 
    def on_touch_up(self, touch):
        if touch in self._touches and touch.grab_state:
            touch.ungrab(self)
            del self._last_touch_pos[touch]
            self._touches.remove(touch)
 
        if self.collide_point(*touch.pos):
            return True
 
    def scale_with_touch(self, touch):
        if len(self._touches) == 1:
            return False
 
        points = [Vector(self._last_touch_pos[t]) for t in self._touches if t is not touch]
        points.append(Vector(touch.pos))
 
        anchor = max(points[:-1], key=lambda p: p.distance(touch.pos))
        farthest = max(points, key=anchor.distance)
        if farthest is not points[-1]:
            return False
 
        old_line = Vector(*touch.ppos) - anchor
        new_line = Vector(*touch.pos) - anchor
        if not old_line.length():
            return False
 
        scale = new_line.length() / old_line.length()
        new_scale = scale * self.font_size
        new_scale = min(self.font_size_max, max(self.font_size_min, new_scale))
        self.font_size = new_scale
        return True

traceback

[INFO              ] [Base        ] Leaving application in progress...
 Traceback (most recent call last):
   File "C:/Users/mike/Dropbox/salesBerry/rev2.py", line 219, in <module>
     Rev2App().run()
   File "C:\Users\mike\Kivy\kivy27\kivy\app.py", line 824, in run
     runTouchApp()
   File "C:\Users\mike\Kivy\kivy27\kivy\base.py", line 487, in runTouchApp
     EventLoop.window.mainloop()
   File "C:\Users\mike\Kivy\kivy27\kivy\core\window\window_sdl2.py", line 525, in mainloop
     self._mainloop()
   File "C:\Users\mike\Kivy\kivy27\kivy\core\window\window_sdl2.py", line 290, in _mainloop
     EventLoop.idle()
   File "C:\Users\mike\Kivy\kivy27\kivy\base.py", line 327, in idle
     Clock.tick()
   File "C:\Users\mike\Kivy\kivy27\kivy\clock.py", line 483, in tick
     self._process_events()
   File "C:\Users\mike\Kivy\kivy27\kivy\clock.py", line 615, in _process_events
     event.tick(self._last_tick, remove)
   File "C:\Users\mike\Kivy\kivy27\kivy\clock.py", line 374, in tick
     ret = callback(self._dt)
   File "C:\Users\mike\Kivy\kivy27\kivy\uix\stacklayout.py", line 263, in do_layout
     c2.pos[innerattr] = u
 TypeError: 'tuple' object does not support item assignment