'module' object has no attribute 'FormatChecker'

after I install the savanna using the setup.py. I start the savanna by

savanna-api --config-file /etc/savanna/savanna.conf

it seems some wrong.

kylin@node1:~$ savanna-api --config-file /etc/savanna/savanna.conf Traceback (most recent call last):
  File "/usr/local/bin/savanna-api", line 5, in <module>
    pkg_resources.run_script('savanna==0.2', 'savanna-api')
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 499, in run_script
    self.require(requires)[0].run_script(script_name, ns)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 1235, in run_script
    execfile(script_filename, namespace, namespace)
  File "/usr/local/lib/python2.7/dist-packages/savanna-0.2-py2.7.egg/EGG-INFO/scripts/savanna-api", line 35, in <module>
    import savanna.main as server
  File "/usr/local/lib/python2.7/dist-packages/savanna-0.2-py2.7.egg/savanna/main.py", line 22, in <module>
    from savanna.api import v10 as api_v10
  File "/usr/local/lib/python2.7/dist-packages/savanna-0.2-py2.7.egg/savanna/api/v10.py", line 18, in <module>
    from savanna.service import validation as v
  File "/usr/local/lib/python2.7/dist-packages/savanna-0.2-py2.7.egg/savanna/service/validation.py", line 23, in <module>
    from savanna.utils import api_validator
  File "/usr/local/lib/python2.7/dist-packages/savanna-0.2-py2.7.egg/savanna/utils/api_validator.py", line 24, in <module>
    @jsonschema.FormatChecker.cls_checks('valid_name')
AttributeError: 'module' object has no attribute 'FormatChecker'

how should i do ? thanks