python beautiful soup error

$ python example6.py
Traceback (most recent call last):
  File "example6.py", line 4, in <module>
    tag = Tag(soup, "a", [("href", 'http://mylink.com')])
  File "/usr/lib/python2.7/dist-packages/bs4/element.py", line 712, in __init__
    self.contains_substitutions = builder.set_up_substitutions(self)
AttributeError: 'str' object has no attribute 'set_up_substitutions'