hide already-awaited coroutines from the user

asynckivy/_core.py

@@ -29,16 +29,23 @@ def step_coro(*args, **kwargs):
 class Task:
     '''(internal)'''
     __slots__ = ('coro', 'done', 'result', 'done_callback')
-    def __init__(self, coro, *, done_callback=None):
-        self.coro = coro
+    def __init__(self):
+        self.coro = None
         self.done = False
         self.result = None
+        self.done_callback = None
+    def run(self, coro, *, done_callback=None):
+        if self.coro is not None:
+            raise Exception("'run()' can be called only once.")
         self.done_callback = done_callback
-    async def _run(self):
-        self.result = await self.coro
+        self.coro = start(self._wrapper(coro))
+    async def _wrapper(self, inner_coro):
+        self.result = await inner_coro
         self.done = True
         if self.done_callback is not None:
             self.done_callback()
+    def cancel(self):
+        self.coro.close()
 
 
 @types.coroutine
@@ -54,9 +61,9 @@ def done_callback():
         n_coros_left -= 1
         if n_coros_left == 0:
             step_coro()
-    tasks = tuple(Task(coro, done_callback=done_callback) for coro in coros)
-    for task in tasks:
-        start(task._run())
+    tasks = tuple(Task() for coro in coros)
+    for task, coro in zip(tasks, coros):
+        task.run(coro, done_callback=done_callback)
 
     if n_coros_left <= 0:
         return tasks

examples/github_issue/#11.py

@@ -0,0 +1,48 @@
+from kivy.lang import Builder
+from kivy.app import App
+from kivy.uix.button import Button
+import asynckivy as ak
+
+
+KV_CODE = '''
+BoxLayout:
+    orientation: 'vertical'
+    Label:
+        id: label
+        font_size: 50
+    Button:
+        id: button
+        font_size: 50
+'''
+
+class TestApp(App):
+    def build(self):
+        return Builder.load_string(KV_CODE)
+    def on_start(self):
+        async def some_task():
+            label = self.root.ids.label
+            button = self.root.ids.button
+            label.text = '--'
+            button.text = 'start spinning'
+            await ak.event(button, 'on_press')
+            button.text = 'stop'
+            tasks = await ak.or_(
+                ak.event(button, 'on_press'),
+                spinning(label),
+            )
+            tasks[1].coro.close()  # 'tasks[1].cancel()' is preferable
+            self.root.remove_widget(button)
+            label.text = 'fin.'
+        ak.start(some_task())
+
+
+async def spinning(label):
+    import itertools
+    sleep_for_10th_of_a_second = await ak.create_sleep(.1)
+    for stick in itertools.cycle('\ | / --'.split()):
+        label.text = stick
+        await sleep_for_10th_of_a_second()
+
+
+if __name__ == '__main__':
+    TestApp().run()