Add possibility of using as decorator

CHANGES/141.feature

@@ -0,0 +1 @@
+`timeout` can now also be used as function decorator.

README.rst

@@ -37,6 +37,13 @@ that cancels a block on *timeout* expiring::
 *timeout* parameter could be ``None`` for skipping timeout functionality.
 
 
+Another possibility is to use ``timeout`` as function decorator::
+
+    @timeout(1.5)
+    async def possibly_long_running():
+        pass
+
+
 Alternatively, ``timeout_at(when)`` can be used for scheduling
 at the absolute time::
 

async_timeout/__init__.py

@@ -128,6 +128,13 @@ async def __aexit__(
         self._do_exit(exc_type)
         return None
 
+    def __call__(self, f):
+        async def inner(*args, **kargs):
+            with self:
+                return await f(*args, **kargs)
+
+        return inner
+
     @property
     def expired(self) -> bool:
         """Is timeout expired during execution?"""

tests/test_timeout.py

@@ -26,6 +26,26 @@ async def long_running_task():
     assert canceled_raised, "CancelledError was not raised"
 
 
+@pytest.mark.asyncio
+async def test_timeout_as_decorator():
+    canceled_raised = False
+
+    @timeout(0.01)
+    async def long_running_task(arg, *, karg):
+        assert arg == 1
+        assert karg == 2
+        try:
+            await asyncio.sleep(10)
+        except asyncio.CancelledError:
+            nonlocal canceled_raised
+            canceled_raised = True
+            raise
+
+    with pytest.raises(asyncio.TimeoutError):
+        await long_running_task(1, karg=2)
+    assert canceled_raised, "CancelledError was not raised"
+
+
 @pytest.mark.asyncio
 async def test_timeout_finish_in_time():
     async def long_running_task():