Hi ros community!
I am not sure if this this can be considered a bug or is the
desired behavior but in my opinion it is not very intuitive:

listener.getLatestCommonTime(target_frame,fixed_frame).to_sec()
returns a reference object in electric.

The below typical pattern does not work with this behavior:

before_common_time = -1.0
end = False
while not end:
     [...]

 latest_commontime=numpy.double(listener.getLatestCommonTime(target_frame,fixed_frame).to_sec())
     if break_condition (latest_common_time,before_common_time):
        end=true
     else:
       before_common_time=latest_common_time


Regards.

-- 
Pablo Iņigo Blasco.
http://geus.wordpress.com