python用多个键填充搁置对象/字典

我有一个 4-gram 列表，我想用它来填充字典对象/shevle 对象：

['I','go','to','work']
['I','go','there','often']
['it','is','nice','being']
['I','live','in','NY']
['I','go','to','work']

这样我们就有了类似的东西：

four_grams['I']['go']['to']['work']=1

任何新遇到的 4-gram 都会用它的四个键填充，值为 1，如果再次遇到它，它的值会递增。

你可以这样做：

import shelve

from collections import defaultdict

db = shelve.open('/tmp/db')

grams = [
    ['I','go','to','work'],
    ['I','go','there','often'],
    ['it','is','nice','being'],
    ['I','live','in','NY'],
    ['I','go','to','work'],
]

for gram in grams:
    path = db.get(gram[0], defaultdict(int))

    def f(path, word):
        if not word in path:
            path[word] = defaultdict(int)
        return path[word]
    reduce(f, gram[1:-1], path)[gram[-1]] += 1

    db[gram[0]] = path

print db

db.close()