What does this function do? what is its purpose?  
  
def mmap_read(path, offset, length):  
    
    with open(path, 'rb') as f:  
        
        mm = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ)  
        mm.seek(offset)  
        
        data = mm.read(length)  
        mm.close()  
        
    return data  

