Python遍歷嵌套字典

Question

首先，這里是問題和編寫的代碼：

def family_lineage(familytree, lineage):
    '''(dict, list of strs) -> boolean
    Return True if lineage specifies a list of names who are directly related
    in a chain of parent-child relationships, and NOT child-parent, parent-grandchild..etc,
    beginning from the first generation listed.

    >>> trace_lineage({'Gina': {'Sam': {'Tina': {}},
                           'Li': {}},
                   'Guy': {}},
                      ['Gina'])
    True

    >>> trace_lineage({'Gina': {'Sam': {'Tina': {}},
                               'Li': {}},
                       'Guy': {}},
                      ['Gina', 'Sam', 'Tina'])
    True
    >>> trace_lineage({'Gina': {'Sam': {'Tina': {}},
                               'Li': {}},
                       'Guy': {}},
                      ['Gina', 'Tina'])
    False
    '''

因此，在上面的示例中，它顯示“ Guy”沒有孩子，而“ Gina”有兩個孩子“ Sam”和“ Li”。 “山姆”有一個孩子“蒂娜”。

for k, v in familytree.items():
    for n, m in v.items():
        if lineage[0] == any(k) and len(lineage) == 1:
            return True
        elif lineage[0] == k and lineage[1] == n and len(lineage) ==2:
            return True
        elif lineage[0] == k and lineage[1] == n and lineage[2] == m and \
        len(lineage) == 3:
            return True
        else:
            return False

因此，我的問題是，如果家族樹擴展到三代以上，我將如何寫呢？ 有沒有更簡潔的代碼編寫方式？

Answer 1

這是一種迭代方法，即使lineage不是從家族樹的頂部開始，也可以使用：

def family_lineage(familytree, lineage):
    trees = [familytree]
    while trees:
        tree = trees.pop()
        trees.extend(t for t in tree.values() if t)
        for name in lineage:
            if name not in tree:
                break
            tree = tree[name]
        else:
            return True
    return False

Answer 2

基本上，您想看看是否可以遍歷樹。 使用reduce()遍歷元素，如果引發KeyError ，則該路徑不存在：

def family_lineage(familytree, lineage):
    if not familytree:
        return False
    try:
        reduce(lambda d, k: d[k], lineage, familytree)
        return True
    except KeyError:
        # No match at this level, recurse down the family tree
        return any(family_lineage(val, lineage) for val in familytree.itervalues())

reduce()從familytree開始，遞歸地將lambda函數應用於lineage 。

為了支持尋找更深層次的譜系樹倒，則需要向下遞歸在樹上KeyError秒。

演示：

>>> tree = {'Gina': {'Sam': {'Tina': {}}, 'Li': {}}, 'Guy': {}}
>>> family_lineage(tree, ['Gina'])
True
>>> family_lineage(tree, ['Gina', 'Sam', 'Tina'])
True
>>> family_lineage(tree, ['Gina', 'Tina'])
False
>>> family_lineage(tree, ['Sam', 'Tina'])
True