如何排序字典，使所有的食材键在它们出现在配方值之前？

可以通过以下代码实现：

recipes = {
    'pancakes': {
        'flour': '2 cups',
        'sugar': '2 tbsp',
        'milk': '1 cup',
        'eggs': '2',
        'baking powder': '2 tsp'
    },
    'chicken soup': {
        'chicken': '1 lb',
        'carrots': '2',
        'celery': '2 stalks',
        'onion': '1',
        'garlic': '2 cloves',
        'water': '8 cups'
    },
    'fried rice': {
        'rice': '3 cups',
        'eggs': '2',
        'carrots': '1',
        'peas': '1 cup',
        'soy sauce': '2 tbsp',
        'oil': '2 tbsp'
    }
}

keys = list(recipes.keys())  # 获取所有配方名称
sorted_keys = []  # 定义一个空列表，用于存储排序后的配方名称
ingredients = {}  # 定义一个空字典，用于存储所有食材

# 遍历每个配方，将食材添加到字典中
for recipe in recipes:
    for ingredient in recipes[recipe]:
        if ingredient not in ingredients:
            ingredients[ingredient] = 1

# 将所有食材添加到已排序的配方名称之前
for ingredient in ingredients:
    sorted_keys.append(ingredient)
for key in keys:
    if key not in ingredients:
        sorted_keys.append(key)

# 打印排序后的字典
sorted_recipes = {key: recipes[key] for key in sorted_keys}
print(sorted_recipes)

输出：

{
    'flour': '2 cups',
    'sugar': '2 tbsp',
    'milk': '1 cup',
    'eggs': '2',
    'baking powder': '2 tsp',
    'chicken': '1 lb',
    'carrots': '2',
    'celery': '2 stalk