Random port binding not showing up in the .attr object

I run a container and use the option ports={8000: None} in order to assign random port binding for this container. I then try to print the container.attr to look for what port did it bind to. It always get empty values: u'PortBindings': {u'8000/tcp': [{u'HostPort': u'', u'HostIp': u''}]}

I use the shell to make sure the container is running and binding ports correctly, and it works just fine. The container is indeed running the ports are bind correctly. But I need to access the port binding from the container object.

What is the problem here?

Start by reproducing the issue with the Python ports={8000: None} option, then compare container.attr with the port information shown by the shell while the container is running. No source file or test is named; done means the container object exposes the assigned random host port consistently with the running container.