Added check for deltatime without hardcoded any strings.

It was hard to not hardcode any strings.

Author: psigen

src/prpy/base/robot.py

@@ -457,7 +457,13 @@ def ExecuteTrajectory(self, traj, defer=False, timeout=None, period=0.01, **kwar
             else:
                 return traj
 
-        # Verify that the trajectory is timed.
+        # Verify that the trajectory is timed by checking whether the first
+        # waypoint has a valid deltatime value.
+        cspec = traj.GetConfigurationSpecification()
+        if cspec.ExtractDeltaTime(traj.GetWaypoint(0)) is None:
+            raise ValueError('Trajectory cannot be executed, it is not timed.')
+
+        # Verify that the trajectory has non-zero duration.
         if traj.GetDuration() <= 0.0:
             import warnings
             warnings.warn('Executing zero-length trajectory. Please update the'