如何在特定嵌套级别筛选嵌套词典？

Question

我想将嵌套字典过滤到某个级别，例如：

d = {'fruit': {'sweet': {'green': 'apple', 'red': 'tomato'}, 'bitter': {'green': 'cucumber'}}}

我想编写一个函数filter_at_level( d, 2, lambda r: r == 'green' )，它只返回以下内容而不修改原始数据：

{'fruit': {'sweet': {'green': 'apple'}, 'bitter': {'green': 'cucumber'}}}

我应该避免递归吗？它能在没有递归的情况下高效地编写吗？你知道吗

Answer 1

from itertools import ifilter

def f(d, func, l):
    if l == 0:
        return {k: d[k] for k in ifilter(func, d)}
    return {k: f(v, func, l - 1) for k, v in d.iteritems()}

d = {'fruit': {'sweet': {'green': 'apple', 'red': 'tomato'}, 'bitter': {'green': 'cucumber'}}}

print f(d, lambda k: k == 'green', 2)

或者如果您不想要空元素：

from itertools import ifilter

def f(d, func, l):
    if l == 0:
        return {k: d[k] for k in ifilter(func, d)}
    tmp = {k: f(v, func, l - 1) for k, v in d.iteritems()}
    return {k: v for k, v in tmp.iteritems() if v}

d = {'fruit': {'sweet': {'green': 'apple', 'red': 'tomato'}, 'bitter': {'green': 'cucumber'}, 'x': {'a': 'z'}}}

print f(d, lambda k: k == 'green', 2)