def __bool__(self):  
return bool(self._db)<EOL>
Return :code:`False` if tree object has no nodes, :code:`True` otherwise.

For example:

    >>> from __future__ import print_function
    >>> import ptrie
    >>> tobj = ptrie.Trie()
    >>> if tobj:
    ...     print('Boolean test returned: True')
    ... else:
    ...     print('Boolean test returned: False')
    Boolean test returned: False
    >>> tobj.add_nodes([{'name':'root.branch1', 'data':5}])
    >>> if tobj:
    ...     print('Boolean test returned: True')
    ... else:
    ...     print('Boolean test returned: False')
    Boolean test returned: True