给定嵌套列表元素，找到一个级别的后退列表值

Question

Say i have List=[[[['a','b'],['c','d'],['e','f']],[['1','2'],['3','4'],['5','6']]],[[['a','b'],['c','d'],['e','f']],[['1','2'],['3','4'],['5','6']]]] i know that if i call List[0][0] i will get [['a', 'b'], ['c', 'd'], ['e', 'f']] , and so on.

Is there any built-in or external python function(suppose its func(a) ) or way to get the nested list element a one level back?

So if i call func(List[0][1]) those function will return List[0] or when i call func(List[1][0][1]) those function will return List[1][0] but if i call func(List) it will return List since it's already at the root. I've been searching for this kind of problem for hours but still couldn't find the solution.

Answer 1

You can use the following recursive function:

def get_parent_list(the_elem, the_list):
    if (the_elem == the_list):
        return (True, the_elem)
    elif the_elem in the_list:
        return (True, the_list)
    else:
        for e in the_list:
            if (type(e) is list):
                (is_found, the_parent) = get_parent_list(the_elem, e)
                if (is_found):
                    return (True, the_parent)
        return (False, None)

Testing it out:

my_list=[[[['a','b'],['c','d'],['e','f']],[['1','2'],['3','4'],['5','6']]],
         [[['a','b'],['c','d'],['e','f']],[['1','2'],['3','4'],['5','6']]]]

Test Case 1:

the_child = my_list[0][1][1]
the_flag, the_parent = get_parent_list(the_child, my_list)
print (the_flag)
print (the_child)
print (the_parent)

Result:

True
['3', '4']
[['1', '2'], ['3', '4'], ['5', '6']]

Test Case 2:

the_child = my_list[0][1]
the_flag, the_parent = get_parent_list(the_child, my_list)
print (the_flag)
print (the_child)
print (the_parent)

Result:

True
[['1', '2'], ['3', '4'], ['5', '6']]
[[['a', 'b'], ['c', 'd'], ['e', 'f']], [['1', '2'], ['3', '4'], ['5', '6']]]

Test Case 3:

the_child = my_list[:]
the_flag, the_parent = get_parent_list(the_child, my_list)
print (the_flag)
print (the_child)
print (the_parent)

Result:

True
[[[['a', 'b'], ['c', 'd'], ['e', 'f']], [['1', '2'], ['3', '4'], ['5', '6']]], [[['a', 'b'], ['c', 'd'], ['e', 'f']], [['1', '2'], ['3', '4'], ['5', '6']]]]
[[[['a', 'b'], ['c', 'd'], ['e', 'f']], [['1', '2'], ['3', '4'], ['5', '6']]], [[['a', 'b'], ['c', 'd'], ['e', 'f']], [['1', '2'], ['3', '4'], ['5', '6']]]]

Test Case 4:

the_child = my_list[0][1] + ['Non-existent value']
the_flag, the_parent = get_parent_list(the_child, my_list)
print (the_flag)
print (the_child)
print (the_parent)

Result:

False
[['1', '2'], ['3', '4'], ['5', '6'], 'Non-existent value']
None