类型 dict：列表值

Question

谁能帮我实现这个功能吗？我不知道如何编写代码，并且我在函数体中编写的内容是错误的。

def get_quantities(table_to_foods: Dict[str, List[str]]) -> Dict[str, int]:

    """The table_to_foods dict has table names as keys (e.g., 't1', 't2', and
    so on) and each value is a list of foods ordered for that table.

    Return a dictionary where each key is a food from table_to_foods and each
    value is the quantity of that food that was ordered.

    >>> get_quantities({'t1': ['Vegetarian stew', 'Poutine', 'Vegetarian stew'],
    't3': ['Steak pie', 'Poutine', 'Vegetarian stew'], 't4': ['Steak pie', 'Steak pie']})
    {'Vegetarian stew': 3, 'Poutine': 2, 'Steak pie': 3}    
    """

    food_to_quantity = {}
    for t in table_to_foods:
        for i in table_to_foods[t]:
            if i in table_to_foods[t]:
                food_to_quantity[i] = food_to_quantity[i] + 1

    return food_to_quantity

Answer 1

itertools.chain如果您喜欢使用and ，这只是另一种方法collections.Counter：

from itertools import chain
from collections import Counter

dict(Counter(chain.from_iterable(foods.values())))
#or Simply
dict(Counter(chain(*foods.values())))

#Output:
#{'apple': 3, 'banana': 4, 'grapes': 1, 'orange': 1}