问题描述:
Write a function to generate a 3d array having each element as '*'.

测试用例:
["assert array_3d(6,4,3)==[[['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*']], [['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*']], [['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*', '*']]]", "assert array_3d(5,3,4)==[[['*', '*', '*', '*', '*'], ['*', '*', '*', '*','*'], ['*', '*', '*', '*', '*']], [['*', '*', '*', '*', '*'],['*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*']], [['*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*']], [['*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*'], ['*', '*', '*', '*', '*']]]", "assert array_3d(1,2,3)==[[['*'],['*']],[['*'],['*']],[['*'],['*']]]"]

生成的代码:
def array_3d(depth, rows, cols):
    return [[['*' for _ in range(cols)] for _ in range(rows)] for _ in range(depth)]