asyn.Event: add .wait method.

Author: peterhinch

PRIMITIVES.md

@@ -205,6 +205,10 @@ Synchronous Methods:
  * `is_set` No args. Returns `True` if the event is set.
  * `value` No args. Returns the value passed to `set`.
 
+Asynchronous Method:
+ * `wait` For CPython compatibility. Pause until event is set. The CPython
+ Event is not awaitable.
+
 The optional data value may be used to compensate for the latency in awaiting
 the event by passing `loop.time()`.
 

asyn.py

@@ -104,6 +104,10 @@ def clear(self):
         self._flag = False
         self._data = None
 
+    async def wait(self):  # CPython comptaibility
+        while not self._flag:
+            await asyncio.sleep_ms(self.delay_ms)
+
     def __await__(self):
         while not self._flag:
             await asyncio.sleep_ms(self.delay_ms)