如何在python外部列表的最后一个嵌套列表中添加项目？

Question

Is thery any nice compact way of adding an item to the last nested list of an outer list. Ie:

a=[1,2,[3,4,[5,6]]] and after the insertion of 7 i want my list to become

a=[1,2,[3,4,[5,6,7]]]

Answer 1

You can use indexing to reference the last inner list:

>>> a=[1,2,[3,4,[5,6]]]
>>> a[2][2].append(7)
>>> a
[1, 2, [3, 4, [5, 6, 7]]]

Or you can write a function to seek out the last inner list:

>>> def findlastlist(s):
    while s and isinstance(s[-1], list):
        s = s[-1]
    return s

>>> a=[1,2,[3,4,[5,6]]]
>>> findlastlist(a).append(7)
>>> a
[1, 2, [3, 4, [5, 6, 7]]]

Answer 2

If you don't look for a general solution:

>>> a=[1,2,[3,4,[5,6]]]
>>> a[-1][-1].append(7)
>>> print a
[1, 2, [3, 4, [5, 6, 7]]]

If you do, here's a naive implementation (for usage, see the doctests):

A function, that returns the nesting level of a list:

def nesting(alist, level=0):
    """ Get the nesting level of a list.

    >>> nesting([])
    0
    >>> nesting([1, 2])
    0
    >>> nesting([1, [2]])
    1
    >>> nesting([1, 2, [3, 4, [5, 6]]])
    2
    >>> nesting([1, 2, [3, 4, [5, 6]], [33, 44, [55, 66]]])
    2
    """
    try:
        alist[-1]
    except IndexError:
        return level
    except TypeError:
        return level - 1
    else:
        return nesting(alist[-1], level=level + 1)

A function, that appends an element to alist at a certain level :

def append_nested(alist, element, level):
    """
    >>> x = []
    >>> append_nested(x, 'hello', nesting(x))
    ['hello']

    >>> x = [1, 2, 3]
    >>> append_nested(x, 'hello', nesting(x))
    [1, 2, 3, 'hello']

    >>> x = [1, 2, 3, [4, 5]]
    >>> append_nested(x, 'hello', nesting(x))
    [1, 2, 3, [4, 5, 'hello']]

    >>> x = [1, 2, 3, [4, 5], [7, 8]]
    >>> append_nested(x, 'hello', nesting(x))
    [1, 2, 3, [4, 5], [7, 8, 'hello']]

    >>> x = [1,2,[3,4,[5,6]]]
    >>> append_nested(x, 7, nesting(x))
    [1, 2, [3, 4, [5, 6, 7]]]

    >>> x = [1,2,[3,4,[5,6]]]
    >>> append_nested(x, 7, 0) # append to the 'root' list
    [1, 2, [3, 4, [5, 6]], 7]
    """
    z = alist
    for i in range(level):
        z = z[-1]
    z.append(element)
    return alist

To test them, just run:

if __name__ == '__main__':
    import doctest
    doctest.testmod()

Answer 3

If you need a general solution try this:

def last_inner_append(x, y):
    try:
        if isinstance(x[-1], list):
            last_inner_append(x[-1], y)
            return x
    except IndexError:
        pass
    x.append(y)
    return x

>>> x = [1,2,[3,4,[5,6]]]
>>> y = 7
>>> last_inner_append(x, y)
[1,2,[3,4,[5,6,7]]]

It recursively works through the final element of nested lists until it reaches something that is not a list. At this point it sticks your value there. The try / except block allows it to handle empty lists.