无法在本地的Google App Engine上的Go中启动演示应用

I followed the tutorial from google here: https://console.developers.google.com/start/appengine

After what I tried started the demo application and got the following error:

$ goapp serve appengine-try-go

Traceback (most recent call last):
  File "/home/nek/google-cloud-sdk/platform/google_appengine/dev_appserver.py", line 83, in <module>
    _run_file(__file__, globals())
  File "/home/nek/google-cloud-sdk/platform/google_appengine/dev_appserver.py", line 79, in _run_file
    execfile(_PATHS.script_file(script_name), globals_)
  File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 36, in <module>
    from google.appengine.tools.devappserver2 import dispatcher
  File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/dispatcher.py", line 29, in <module>
  from google.appengine.tools.devappserver2 import module
  File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/module.py", line 71, in <module>
  from google.appengine.tools.devappserver2 import vm_runtime_factory
File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/vm_runtime_factory.py", line 25, in <module>
  from google.appengine.tools.devappserver2 import vm_runtime_proxy
File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/vm_runtime_proxy.py", line 29, in <module>
  from google.appengine.tools.devappserver2 import log_manager
File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/log_manager.py", line 34, in <module>
  from google.appengine.tools.docker import containers
File "/home/nek/google-cloud-sdk/platform/google_appengine/google/appengine/tools/docker/containers.py", line 47, in <module>
  import docker
ImportError: No module named docker
error while running dev_appserver.py: exit status 1

I'm using it on Ubuntu 14.04 with zsh and python 2.7.6.

Does somebody understand why ?

After installed pip, I executed the following command:

sudo pip install docker-py

Now it works.