Document PeriodicCallback.is_running.

diff --git a/tornado/ioloop.py b/tornado/ioloop.py
index 52b73ad5bf504aa834c9d81417de2aed40466e90..bbe74a15a326a27f9ff51c3938ce02d50db6af8f 100644 (file)
--- a/tornado/ioloop.py
+++ b/tornado/ioloop.py
@@ -970,6 +970,10 @@ class PeriodicCallback(object):
             self._timeout = None
 
     def is_running(self):
+        """Return True if this `.PeriodicCallback` has been started.
+
+        .. versionadded:: 4.1
+        """
         return self._running
 
     def _run(self):