handle short-circuit in wait_for_engines(block=False)

Author: minrk

ipyparallel/client/client.py

@@ -1334,7 +1334,12 @@ def wait_for_engines(self, n, *, timeout=-1, block=True):
         TimeoutError : if timeout is reached.
         """
         if len(self.ids) >= n:
-            return
+            if block:
+                return
+            else:
+                f = Future()
+                f.set_result(None)
+                return f
         tic = now = time.perf_counter()
         if timeout >= 0:
             deadline = tic + timeout
@@ -1363,7 +1368,7 @@ def on_timeout():
             else:
                 future.set_exception(
                     TimeoutError(
-                        "{n} engines not ready in {timeout} seconds. Currently ready: {len(self.ids)}"
+                        f"{n} engines not ready in {timeout} seconds. Currently ready: {len(self.ids)}"
                     )
                 )
 

ipyparallel/tests/test_client.py

@@ -646,6 +646,11 @@ def test_local_ip_true_doesnt_trigger_warning(self):
     def test_wait_for_engines(self):
         n = len(self.client)
         assert self.client.wait_for_engines(n) is None
+
+        f = self.client.wait_for_engines(n, block=False)
+        assert isinstance(f, Future)
+        assert f.done()
+
         with pytest.raises(TimeoutError):
             self.client.wait_for_engines(n + 1, timeout=0.1)