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It is most likely being published, but only once, and too fast after creating the Publisher. This doesn't leave any time for any potential Subscribers to actually notice it, register, prepare to receive the data and then actually receive it.

If you want to give "late joiners" a chance to receive the message -- and you don't publish periodically, or have messages changing contents often, you could try using a latched Publisher. From wiki/rospy/Overview/Publishers and Subscribers: rospy.Publisher initialization:

There are additional advanced options that allow you to configure the Publisher:

[..]

latch=False

Enable 'latching' on the connection. When a connection is latched, a reference to the last message published is saved and sent to any future subscribers that connect. This is useful for slow-changing or static data like a map. The message is not copied! If you change the message object after publishing, the change message will be sent to future subscribers.

Note how publishing data "like a map" is given as one of the cases in which this could be useful.

It is most likely being published, but only once, and too fast after creating the Publisher. This doesn't leave any time for any potential Subscribers to actually notice it, register, prepare to receive the data and then actually receive it.

If you want to give "late joiners" a chance to receive the message -- and you don't publish periodically, or have messages changing contents often, you could try using a latched Publisher. From wiki/rospy/Overview/Publishers and Subscribers: rospy.Publisher initialization:

There are additional advanced options that allow you to configure the Publisher:

[..]

• latch=False

  Enable 'latching' on the connection. When a connection is latched, a reference to the last message published is saved and sent to any future subscribers that connect. This is useful for slow-changing or static data like a map. The message is not copied! If you change the message object after publishing, the change message will be sent to future subscribers.

Note how publishing data "like a map" is given as one of the cases in which this could be useful.