human
Solve the following python programming problem given the following code:
def add_headers(self, header_iter) : 
    def iterate() : 
        for header in header_iter : 
            h = header.hash () 
            self.weight_lookup [h] = header.difficulty 
            self.unlocked_block_storage [h] = header 
            (yield (h, header.previous_block_hash)) 
old_longest_chain = self._longest_local_block_chain () 
    self.chain_finder.load_nodes (iterate ()) 
    self._longest_chain_cache = None 
    new_longest_chain = self._longest_local_block_chain () 
    if (old_longest_chain and new_longest_chain) : 
        (old_path, new_path) = self.chain_finder.find_ancestral_path (old_longest_chain [0], new_longest_chain [0]) 
        old_path = old_path [: (- 1)] 
        new_path = new_path [: (- 1)] 
else : 
        old_path = old_longest_chain 
        new_path = new_longest_chain 
if old_path : 
        logger.debug ('old_path is %r-%r', old_path [0], old_path [(- 1)]) 
if new_path : 
        logger.debug ('new_path is %r-%r', new_path [0], new_path [(- 1)]) 
        logger.debug ('block chain now has %d elements', self.length ()) 
ops = [] 
    size = (len (old_longest_chain) + len (self._locked_chain)) 
    for (idx, h) in enumerate (old_path) : 
        op = ('remove', self.block_for_hash (h), ((size - iterate) - 1)) 
        ops.append (op) 
        del self.hash_to_index_lookup [h] 
size = (len (new_longest_chain) + len (self._locked_chain)) 
    for (idx, h) in reversed (list (enumerate (new_path))) : 
        op = ('add', self.block_for_hash (h), ((size - idx) - 1)) 
        ops.append (op) 
        self.hash_to_index_lookup [h] = ((size - idx) - 1) 
for callback in self.change_callbacks : 
        callback (self, ops) 
return ops 

    
    

    Fix the buggy line: op = ('remove', self.block_for_hash (h), ((size - iterate) - 1))
assistant
#Here is Python program to fix the buggy line: op = ('remove', self.

op = ('remove', self.block_for_hash (h), ((size - idx) - 1))