human
Solve the following python programming problem given the following code:
def concatenate_events(events, block_lens) : 
    'Concatenate events indexing different runs.' 
    def shift_events(events, offset) : 
        events = events.copy () 
        events [1 :] += offset 
        return events 
offset = np.cumsum (([0] + o [: (- 1)])) 
    return np.hstack ([shift_events (be, o) for (be, o) in zip (events, offset)]) 

    
    

    Fix the buggy line: offset = np.cumsum (([0] + o [: (- 1)]))
assistant
#Here is Python code to fix the buggy line: offset = np.

offset = np.cumsum (([0] + block_lens [: (- 1)]))