【问题标题】：changing values in nested json file with a recursive function in Python在 Python 中使用递归函数更改嵌套 json 文件中的值
【发布时间】：2018-09-18 14:28:15
【问题描述】：

您好，我想创建一个递归函数，该函数可以获取由嵌套 json 文件制成的字典，并将 json 文件中某个属性（属性权重）的所有值乘以 10。

我知道这可以通过其他方式解决（例如正则表达式），但我这样做是为了提高我编写递归函数的能力，所以我想找到一个递归解决方案。

示例输入 json 文件：

    {
      "name": "Entire genepool",
      "children": [{
        "name": "child1",
        "weight": 80,
        "children": [{
          "name": "childAA",
          "weight": 100,
          "children": [{
            "name": "childCC",
            "weight": 60,
            "children": []
          }, {
            "name": "grandchild",
            "weight": 40,
            "children": []
          }]
        }]
      }, {
        "name": "childb",
        "weight": 20,
        "children": []
      }]
    }

这是我到目前为止所做的（Python 2.7），它不起作用，它返回一个空列表，我添加了一个打印语句来可视化输入字典如何通过递归进行更改：

    def recur(dict1):
        print dict1
        print 
        """
        it multiplies * 10 weight attribute in nested json file
        """
        # reduce on step closer to solution
        if not isinstance(dict1, list):
            for key , content in dict1.iteritems():
                if key == "weight":
                    dict1["weight"] = dict1["weight"]*10 
            for key , content in dict1.iteritems():
                if key == "children":
                    simpler_dict = dict1["children"]
                    return  recur(simpler_dict)
        else:
            if len(dict1) < 1:
                return dict1
            else:
                for sub_dict in dict1:
                    for key , content in sub_dict.iteritems():
                        if key == "weight":
                            sub_dict["weight"] = sub_dict["weight"]*10 
                    for key , content in sub_dict.iteritems():
                        if key == "children":
                            simpler_dict2 = sub_dict["children"]
                            return  recur(simpler_dict2)

打开文件将其转换为字典并调用函数

with open("tree_rec.json", "r") as f:
    tree_dic = json.load(f)
recur(tree_dic)

每次递归的输入

  {u'name': u'Entire genepool', u'children': [{u'name': u'child1', u'weight': 80, u'children': [{u'name': u'childAA', u'weight': 100, u'children': [{u'name': u'childCC', u'weight': 60, u'children': []}, {u'name': u'grandchild', u'weight': 40, u'children': []}]}]}, {u'name': u'childb', u'weight': 20, u'children': []}]}

  [{u'name': u'child1', u'weight': 80, u'children': [{u'name': u'childAA', u'weight': 100, u'children': [{u'name': u'childCC', u'weight': 60, u'children': []}, {u'name': u'grandchild', u'weight': 40, u'children': []}]}]}, {u'name': u'childb', u'weight': 20, u'children': []}]

  [{u'name': u'childAA', u'weight': 100, u'children': [{u'name': u'childCC', u'weight': 60, u'children': []}, {u'name': u'grandchild', u'weight': 40, u'children': []}]}]

  [{u'name': u'childCC', u'weight': 60, u'children': []}, {u'name': u'grandchild', u'weight': 40, u'children': []}]

  []

它返回一个空列表：[]

【问题讨论】：

“不起作用”是对问题最没有用的描述。请解释它“不起作用”的方式（如果您遇到异常，请发布确切的错误消息和完整的回溯。
哦，是的：你甚至没有展示你是如何调用那个函数的......
请提供minimal reproducible example
添加print 语句来跟踪您的函数的执行或在步进调试器中运行它（docs.python.org/2/library/pdb.html），问题应该非常明显。提示：编写你的函数，使其要么改变它的输入并且不返回任何内容，要么（排他的“或”）创建一个新的（修改后的）字典并返回它，但不要试图混合两者。

标签： python json recursion nested

【解决方案1】：

我想你正在寻找的递归可以这样实现：

def main_caller(json_file):
    if "weight" in json_file:
        json_file["weight"] *= 10
    if "children" in json_file and json_file["children"]:
        for child_index , children in enumerate(json_file["children"]):
            json_file["children"][child_index] = main_caller(children)
    return json_file

【讨论】：

【解决方案2】：

您只需要在 dicts 中查找“权重”键并遍历所有列表，您的 recur 函数可以简单得多：

x =  {"name": "Entire genepool", ...}

def recur(data):
    if isinstance(data, dict):
        for key, value in data.items():
            if key == 'weight':
              data[key] = value*10
            elif isinstance(value, list):
              for i, item in enumerate(value):
                value[i] = recur(item)
        return data

result = recur(x)

结果：

{
    "children": [
        {
            "children": [
                {
                    "children": [
                        {
                            "children": [],
                            "name": "childCC",
                            "weight": 600
                        },
                        {
                            "children": [],
                            "name": "grandchild",
                            "weight": 400
                        }
                    ],
                    "name": "childAA",
                    "weight": 1000
                }
            ],
            "name": "child1",
            "weight": 800
        },
        {
            "children": [],
            "name": "childb",
            "weight": 200
        }
    ],
    "name": "Entire genepool"
}

【讨论】：