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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def namedb_get_all_preordered_namespace_hashes( cur, current_block ):
 """ Get a list of all preordered namespace hashes that haven't expired yet. Used for testing """

    query = "SELECT preorder_hash FROM preorders WHERE op = ? AND block_number >= ? AND block_number < ?;"
    args = (NAMESPACE_PREORDER, current_block, current_block + NAMESPACE_PREORDER_EXPIRE )

    namespace_rows = namedb_query_execute( cur, query, args )
    ret = []
    for namespace_row in namespace_rows:
        ret.append( namespace_row['preorder_hash'] )

    return ret