def get_vars(n):
op = n[<NUM_LIT:0>]<EOL>if op.startswith('<STR_LIT:_>') and op.endswith('<STR_LIT:_>'):<EOL><INDENT>op = op.strip('<STR_LIT:_>')<EOL>if op == '<STR_LIT>':<EOL><INDENT>return [n[<NUM_LIT:1>]]<EOL><DEDENT>return []<EOL><DEDENT>else:<EOL><INDENT>ret = []<EOL>for c in n[<NUM_LIT:1>:]:<EOL><INDENT>vs = get_vars(c)<EOL>if vs:<EOL><INDENT>ret.extend(vs)<EOL><DEDENT><DEDENT>return ret<EOL><DEDENT>
extract variables from expression node
defined by tuple-pair: (_var_, [variable name])