from BTreeWordFinder import *
from BalancedBTree import *
class BalancedBTreeWordFinder(BTreeWordFinder):
'' 'binary search class implemented with a balanced binary tree; inherits from BTreeWordFinder and thus takes advantage of its methods' ''
def __init__(self, file, btree=None):
'' 'Builder methods' ''
BTreeWordFinder.__init__(self, file, btree)
@staticmethod
def main():
'' 'main method version of the class for the search engine implemented with a balanced tree' ''
b = BalancedBTreeWordFinder(BalancedBTreeWordFinder.askFile(), BalancedBTree())
b.findOcurrencesInFile('dictionary.txt')
b.viewIndex()
b.showDepth()
if __name__ == "__main__":
BalancedBTreeWordFinder.main()

def __str__(self):
return str(self._val) # here is the error

Error:
Traceback (most recent call last):
File "D:/btree-word-finder-master/btree-word-finder-master/Code_and_texts/BalancedBTreeWordFinder.py", line 20, in <module>
BalancedBTreeWordFinder.main()
File "D:/btree-word-finder-master/btree-word-finder-master/Code_and_texts/BalancedBTreeWordFinder.py", line 16, in main
b.viewIndex()
File "D:\btree-word-finder-master\btree-word-finder-master\Code_and_texts\BTreeWordFinder.py", line 48, in viewIndex
self.getBTree().doinOrden()
File "D:\btree-word-finder-master\btree-word-finder-master\Code_and_texts\BTree.py", line 80, in doinOrden
self.inOrden(self.getRoot())
File "D:\btree-word-finder-master\btree-word-finder-master\Code_and_texts\BTree.py", line 89, in inOrden
self.visit(probe) # visit mean to search on traversed left
File "D:\btree-word-finder-master\btree-word-finder-master\Code_and_texts\BTree.py", line 107, in visit
print(node)
File "D:\btree-word-finder-master\btree-word-finder-master\Code_and_texts\Node.py", line 39, in __str__
return '%s %s %s'%(self._val)
TypeError: __str__ returned non-string (type tuple)

str(sel._val)  '%s %s %s'%(self._val)
, return '{} {} {}'.format(self._val) and template = '{self._val}'
    return template.format(self)
def __str__(self):
return str(self._val) # here is the error