Error running maltrieve.py

[andr6]

./maltrieve.py
Traceback (most recent call ast):
File "./maltrieve.py", line 38, in
from bs4 import BeautifulSoup
File "/usr/local/lib/python2.7/dist-packages/gevent/builtins.py", line 93, in import
result = _import(_args, *_kwargs)
File "/usr/lib/python2.7/dist-packages/bs4/init.py", line 29, in
from .builder import builder_registry
File "/usr/local/lib/python2.7/dist-packages/gevent/builtins.py", line 93, in import
result = _import(_args, *_kwargs)
File "/usr/lib/python2.7/dist-packages/bs4/builder/init.py", line 306, in
from . import _html5lib
File "/usr/local/lib/python2.7/dist-packages/gevent/builtins.py", line 93, in import
result = _import(_args, *_kwargs)
File "/usr/lib/python2.7/dist-packages/bs4/builder/_html5lib.py", line 57, in
class TreeBuilderForHtml5lib(html5lib.treebuilders._base.TreeBuilder):
AttributeError: 'module' object has no attribute '_base'