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python - 迭代替换json文件中的值

问题描述

我必须执行一些测试来调整 json 文件的一些数字参数。为简单起见，我将所有这些值替换为字符串“变量”，然后执行以下操作：

numeric_vals = [10,20, 30, 40]  # numeric values to replace in that order 
with open ('mypath') as my_file:
    json_str = my_file.read()
for i in numeric_vals:
    json_str = json_str.replace("\"variable\"", str(i), 1)
c = json.loads(json_str)  #loading in order to work with

这工作正常，但有没有更有效的方法来做到这一点？需要替换的值的深度是可变的，并且可能在列表中等。我的 json 文件是 15Kb，我需要测试很多（真的很多！）配置。在每次测试中，大约需要替换 200 个变量。我在 python 2.7 上，但 python 3.5 也是一个选项。谢谢你的帮助！

编辑 ：

这是我的字典样本。需要注意的是，真实的东西要更长更深：

 {
"1": {
    "transition": {
        "value": "variable", # edit here
        "unite": "sec"
    },
    "sequence": [
        {
            "step": "STEP",
            "name": "abc",
            "transition": {
                "value": "variable", #edit here
                "unite": "sec"
            },
            "entity": "aa",
            "_equipement": 3,
            "_value": 0
        },
        {
            "step": "FORK",
            "BRANCHES": [
                {
                    "": {
                        "sequence": [
                            {
                                "step": "STEP",
                                "name": "klm",
                                "transition": {
                                    "value": "variable", # edit here
                                    "unite": "sec"
                                },
                                "entity": "vvv",
                                "_equipement": 10,
                                "_value": 0,
                                "conditions": [
                                    [
                                        {
                                            "name": "ddd",
                                            "type": "el",
                                            "_equipement": 7,
                                            "_value": 1
                                        }
                                    ]
                                ]
                            }
                        ]
                    }
                },
                {
                    "SP": {
                        "sequence": [
                            {
                                "step": "STEP",
                                "name": "bbb",
                                "transition": {
                                    "value": "variable", # edit here
                                    "unite": "sec"
                                },
                                "entity": "bb",
                                "_equipement": 123,
                                "_value": 0,
                                "conditions": [
                                    [
                                        {
                                            "name": "abcd",
                                            "entity": "dgf",
                                            "type": "lop",
                                            "_equipement": 7,
                                            "_valeur": 0
                                        }
                                    ]
                                ]
                            }
                        ]
                    }
                }
            ]
        }
    ]
}

}

标签： python

解决方案

It's generally a bad idea to do string operations on hierarchical/structured data as there may be many cases where you can break the structure. Since you're already parsing your JSON you can extend the decoder to specifically deal with your case during parsing, e.g.:

numeric_vals = [10, 20, 30, 40]  # numeric values to replace in that order

SEARCH = 'variable'
REPLACE = iter(numeric_vals)  # turn into an iterator for sequential access

def replace_values(value):
    return {k: next(REPLACE) if v == SEARCH else v for k, v in value.items()}

with open('path/to/your.json') as f:
    a = json.JSONDecoder(object_hook=replace_values).decode(f.read())

This ensures you're properly parsing your JSON and that it won't replace, for example, a key that happens to be called 'variable'.

Beware, tho, that it will raise an StopIteration exception if there are more "variable" values in the JSON than there are numeric_vals - you can unravel the dict comprehension in replace_values and deal with such case if you expect to encounter such occurrences.

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