python：将for循环转换为递归函数

Question

首先，我还是 python 的新手，所以请放轻松。

我已经完成了我的研究，并且对如何编写递归函数有了基本的了解，但是我对摆在我面前的任务完全感到困惑。

我真的很想得到一些提示和指示，这样我就可以自己做这件事来真正理解。

这是任务：

1. 遍历字典
2. 检查是否有“儿童”键
3. 如果是真的，做点什么
4. 重复

问题来了，

“option”键嵌套在另一个名为“children”的键中。在那里，我想遍历每个“子”键，直到它们不再存在。

这是没有递归的代码的样子。当然它失败了，因为它太解释了，太死板了。

#level(one/two/three) refer to the level of nesting, easier for me to know where I am     in the loop.
#qdf_v2 is a particular type of file which is essentially a dictionary 

for levelone in qdf_v2['children']:
    if 'children' in levelone:
        store = options
        for leveltwo in levelone['children']:
            if 'children' in leveltwo:
                store = options
                for levelthree in leveltwo['children']:
                    if 'children' in levellevel:
                        repeat....

我想遍历字典，它是“儿童”键，直到它们不再存在。

这里有一些 JSON，您可以复制并粘贴到 http://www.jsoneditoronline.org/ 中以查看我正在处理的内容。

{
    "base": "http://panoptic-fearless.ldc.yougov.net/questionnaires/Test_maj_demo_newG4_2/versions/12/",
    "children": [
        {
            "name": "one",
            "children": [
                {
                    "name": "measures",
                    "children": [
                        {
                            "type": "single",
                            "options": {
                                "sort_order": "asending",
                                "chart_layout": "5",
                                "chart_type": "bar",
                                "chart_color": "green"
                            },
                            "text": "How much would you say you like or dislike P.E. at school? ",
                            "name": "KYS_Q1",
                            "responses": {
                                "items": [
                                    {
                                        "code": 1,
                                        "text": "I love it",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 2,
                                        "text": "I like it",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 3,
                                        "text": "I don’t like it",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 4,
                                        "text": "I hate it",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 5,
                                        "text": "Don’t know",
                                        "element": "qdf:response"
                                    }
                                ],
                                "element": "qdf:response_group"
                            },
                            "element": "qdf:question",
                            "export": [
                                {
                                    "name": "KYS_Q1"
                                }
                            ]
                        },
                        {
                            "children": [
                                {
                                    "type": "single",
                                    "options": {
                                        "sort_order": "asending",
                                        "chart_layout": "4",
                                        "chart_type": "pie",
                                        "chart_color": "pink"
                                    },
                                    "text": "{multiple order=\"randomize\" max=3} You said that you $event P.E. at school...<br/> Which THREE of the following are your MAIN reasons for not liking P.E. at school? (Please tick up to three options)",
                                    "name": "KYS_Q2",
                                    "responses": {
                                        "items": [
                                            {
                                                "code": 1,
                                                "text": "I don't like going outside in bad weather (e.g. in the cold, rain etc.)",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 2,
                                                "text": "I’m always picked last to join a team",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 3,
                                                "text": "I don't like my P.E. teacher/ don’t think they are very good",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 4,
                                                "text": "I’m not very good at it",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 5,
                                                "text": "I find the games/ sports we play boring",
                                                "element": "qdf:response"
                                            }
                                        ],
                                        "element": "qdf:response_group"
                                    },
                                    "element": "qdf:question",
                                    "export": [
                                        {
                                            "name": "KYS_Q2"
                                        }
                                    ]
                                },
                                {
                                    "type": "single",
                                    "options": {
                                        "sort_order": "asending",
                                        "chart_layout": "5",
                                        "chart_type": "line",
                                        "chart_color": "green"
                                    },
                                    "text": "{multiple order=\"randomize\"} Below are some feelings that people can have about doing P.E. at school...<br/> Which of the following words describe how you feel about doing P.E. at school? (Please tick all that apply) ",
                                    "name": "KYS_Q3A",
                                    "responses": {
                                        "items": [
                                            {
                                                "code": 1,
                                                "text": "Stressed",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 2,
                                                "text": "Scared",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 3,
                                                "text": "Worried",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 4,
                                                "text": "Sick",
                                                "element": "qdf:response"
                                            },
                                            {
                                                "code": 5,
                                                "text": "Tiring ",
                                                "element": "qdf:response"
                                            }
                                        ],
                                        "element": "qdf:response_group"
                                    },
                                    "element": "qdf:question",
                                    "export": [
                                        {
                                            "name": "KYS_Q3A"
                                        }
                                    ]
                                }
                            ],
                            "element": "qdf:section"
                        },
                        {
                            "type": "single",
                            "options": {
                                "sort_order": "desending",
                                "chart_layout": "5",
                                "chart_type": "bar",
                                "chart_color": "green"
                            },
                            "text": "{single order=\"randomize\"} You said that you $event P.E...<br/> Which ONE of the following is the main reason you like it? ",
                            "name": "KYS_Q4",
                            "responses": {
                                "items": [
                                    {
                                        "code": 1,
                                        "text": "I like getting outside/ not being in the classroom",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 2,
                                        "text": "I like my P.E. teacher",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 3,
                                        "text": "I’m good at it",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 4,
                                        "text": "I find the games/ sports fun",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 5,
                                        "text": "I find the games/ sports easy",
                                        "element": "qdf:response"
                                    }
                                ],
                                "element": "qdf:response_group"
                            },
                            "element": "qdf:question",
                            "export": [
                                {
                                    "name": "KYS_Q4"
                                }
                            ]
                        }
                    ],
                    "element": "qdf:page"
                }
            ],
            "element": "qdf:module"
        },
        {
            "name": "two",
            "children": [
                {
                    "name": "test",
                    "children": [
                        {
                            "type": "single",
                            "options": {
                                "sort_order": "asending",
                                "chart_layout": "5",
                                "chart_type": "bar",
                                "chart_color": "green"
                            },
                            "text": "{multiple order=\"randomize\"}Below are some feelings that people can have about doing P.E at school...<br/> Which of the following words describe how you feel about doing P.E. at school? (Please tick all that apply)   ",
                            "name": "KYS_Q5A",
                            "responses": {
                                "items": [
                                    {
                                        "code": 1,
                                        "text": "Energised/ Awake",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 2,
                                        "text": "Excited",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 3,
                                        "text": "Relaxed",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 4,
                                        "text": "Confident",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 5,
                                        "text": "Happy",
                                        "element": "qdf:response"
                                    }
                                ],
                                "element": "qdf:response_group"
                            },
                            "element": "qdf:question",
                            "export": [
                                {
                                    "name": "KYS_Q5A"
                                }
                            ]
                        },
                        {
                            "type": "single",
                            "options": {
                                "sort_order": "asending",
                                "chart_layout": "25",
                                "chart_type": "column",
                                "chart_color": "orange"
                            },
                            "text": "{multiple order=\"randomize\"} For the following question please do not be afraid to be as honest as possible, no one else will be told your personal answers. <br/> Which of the following have you EVER done in order to avoid taking part in P.E. at school? (Please tick all that apply) ",
                            "name": "KYS_Q6",
                            "responses": {
                                "items": [
                                    {
                                        "code": 1,
                                        "text": "Lied about forgetting my kit",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 2,
                                        "text": "Lied about an injury",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 3,
                                        "text": "Lied about feeling unwell",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 4,
                                        "text": "Faked a note from my parents/ guardian",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 5,
                                        "text": "Faked a note from my doctor/ health professional",
                                        "element": "qdf:response"
                                    }
                                ],
                                "element": "qdf:response_group"
                            },
                            "element": "qdf:question",
                            "export": [
                                {
                                    "name": "KYS_Q6"
                                }
                            ]
                        },
                        {
                            "type": "single",
                            "options": {
                                "sort_order": "asending",
                                "chart_layout": "5",
                                "chart_type": "bar",
                                "chart_color": "green"
                            },
                            "text": "{multiple order=\"randomize\"} For the following question, please think about the teacher who has taught you P.E. MOST recently and if you have more than one teacher teaching you P.E. please think about the one who has taught you most often. <br/>  Which of the following statements do you agree with? (Please tick all that apply)",
                            "name": "KYS_Q7",
                            "responses": {
                                "items": [
                                    {
                                        "code": 1,
                                        "text": "My P.E. teacher inspires me to do more exercise",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 2,
                                        "text": "My P.E. teacher motivates me to take part in P.E. lessons",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 3,
                                        "text": "My P.E. teacher scares me",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 4,
                                        "text": "My P.E. teacher makes P.E. boring",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 5,
                                        "text": "My P.E. teacher makes P.E. fun",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 6,
                                        "text": "My P.E. teacher makes P.E. difficult/ hard",
                                        "element": "qdf:response"
                                    }
                                ],
                                "element": "qdf:response_group"
                            },
                            "element": "qdf:question",
                            "export": [
                                {
                                    "name": "KYS_Q7"
                                }
                            ]
                        },
                        {
                            "type": "single",
                            "options": {
                                "sort_order": "asending",
                                "chart_layout": "5",
                                "chart_type": "bar",
                                "chart_color": "green"
                            },
                            "text": "{multiple order=\"randomize\"} What would make you like P.E. more? (Please tick all that apply)",
                            "name": "KYS_Q8",
                            "responses": {
                                "items": [
                                    {
                                        "code": 1,
                                        "text": "If the P.E. teacher was nicer to me",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 2,
                                        "text": "If more lessons took place indoors (e.g. in the sports hall or a gym)",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 3,
                                        "text": "If more lessons took place outdoors",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 4,
                                        "text": "If we did more interesting sports/ activities",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 5,
                                        "text": "If we had more choice of the types of sport we had to do",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "code": 6,
                                        "text": "If we could wear what we wanted for the lesson",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "options": {
                                            "fixed": true
                                        },
                                        "children": [
                                            {
                                                "export": [
                                                    {
                                                        "name": "KYS_Q8other"
                                                    }
                                                ],
                                                "name": "KYS_Q8other",
                                                "type": "open",
                                                "element": "qdf:question"
                                            }
                                        ],
                                        "code": 7,
                                        "text": "Other ",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "options": {
                                            "xor": true,
                                            "fixed": true
                                        },
                                        "code": 8,
                                        "text": "Don’t know",
                                        "element": "qdf:response"
                                    },
                                    {
                                        "options": {
                                            "xor": true,
                                            "fixed": true
                                        },
                                        "code": 9,
                                        "text": "Not applicable – nothing would make me like P.E. more than I already do",
                                        "element": "qdf:response"
                                    }
                                ],
                                "element": "qdf:response_group"
                            },
                            "element": "qdf:question",
                            "export": [
                                {
                                    "name": "KYS_Q8"
                                }
                            ]
                        }
                    ],
                    "element": "qdf:page"
                }
            ],
            "element": "qdf:module"
        },
        {
            "children": [
                {
                    "children": [
                        {
                            "text": "​\n",
                            "element": "qdf:text"
                        }
                    ],
                    "element": "qdf:page"
                }
            ],
            "element": "qdf:module"
        }
    ],
    "panelid": 13,
    "created": "#2014-01-10T15:57:18.594000+00:00#",
    "typespec": {
        "src": "/questionnaires/typespecs/initial.qdf",
        "element": "qdf:typespec"
    },
    "qdf-ext:ext": [
        "meaningful-page-names"
    ],
    "element": "qdf:questionnaire",
    "builtin": {
        "src": "/questionnaires/builtins/initial.qdf",
        "element": "qdf:typedef"
    },
    "committer": "majeed.sahebzadha",
    "name": "Test_maj_demo_newG4_2",
    "commit message": "added a new module within a module"
}

Answer 1

我会这样处理：

def recursive(input, output=None):
    if output is None:
        output = {} # container to store results
    if 'children' in input:
        # do whatever, add things to output
        recursive(input['children'], output)
    return output

这样，output 字典可以在所有迭代深度中访问，并在最后获得带有所有内容的 returned。这意味着您不必显式处理递归调用的 return 值。

根据您所拥有的具体情况，它可能看起来更像：

def recursive(input, output=None):
    if output is None:
        output = {} # container to store results
    if 'children' in input:
        for child in input['children']:
            # do whatever, add things to output
            recursive(child, output)
    return output    

而output 可能是不同的容器（例如list、set）。

Answer 2

def recurseDict(dictionary):
    if "children" in dictionary:
        return recurseDict(dictionary['children'])
    else:
        return "Whatever you want to return here -- you didn't specify"

这将获取一个字典，检查 "children" 是否是它的键之一，然后递归遍历字典 dictionary['children'] 等等，直到它到达没有 'children' 键的地步（例如字典没有更多的分支）它进入else 分支，你可以返回任何你想要的东西——你没有指定。

Answer 3

这是一个递归遍历字典的示例方法，假设每个孩子也是一个字典：

def compute(my_dict):
    if 'children' in my_dict:
        print my_dict['children']
        for child in my_dict['children']:
            compute(child)