使用JSON模块进行漂亮打印时，如何实现自定义缩进? [英] How to implement custom indentation when pretty-printing with the JSON module?

问题描述

所以我正在使用Python 2.7，使用json模块对以下数据结构进行编码:

So I'm using Python 2.7, using the json module to encode the following data structure:

'layer1': {
    'layer2': {
        'layer3_1': [ long_list_of_stuff ],
        'layer3_2': 'string'
    }
}

我的问题是我正在使用漂亮的打印来打印所有内容，如下所示:

My problem is that I'm printing everything out using pretty printing, as follows:

json.dumps(data_structure, indent=2)

这很棒，除了"layer3_1"中的内容外，我都希望全部缩进-这是一个庞大的字典，列出了坐标，因此，在每个字典上设置一个值就可以很漂亮地打印出一个文件，数千行，示例如下:

Which is great, except I want to indent it all, except for the content in "layer3_1" — It's a massive dictionary listing coordinates, and as such, having a single value set on each one makes pretty printing create a file with thousands of lines, with an example as follows:

{
  "layer1": {
    "layer2": {
      "layer3_1": [
        {
          "x": 1,
          "y": 7
        },
        {
          "x": 0,
          "y": 4
        },
        {
          "x": 5,
          "y": 3
        },
        {
          "x": 6,
          "y": 9
        }
      ],
      "layer3_2": "string"
    }
  }
}

我真正想要的是与以下内容相似的东西:

What I really want is something similar to the following:

{
  "layer1": {
    "layer2": {
      "layer3_1": [{"x":1,"y":7},{"x":0,"y":4},{"x":5,"y":3},{"x":6,"y":9}],
      "layer3_2": "string"
    }
  }
}

我听说可以扩展json模块:是否可以将其设置为仅在"layer3_1"对象内部时关闭缩进?如果是这样，有人可以告诉我如何吗?

I hear it's possible to extend the json module: Is it possible to set it to only turn off indenting when inside the "layer3_1" object? If so, would somebody please tell me how?

推荐答案

已更新

以下是我的原始答案的一个版本，该版本已进行了多次修订.与原始文章不同，我只发布了原始文章，以展示如何在JFSebastian的 answer 中获得第一个想法，并且喜欢他的对象返回了一个不缩进的 string 表示形式.最新的更新版本返回隔离格式的Python对象JSON.

Below is a version of my original answer that has been revised several times. Unlike the original, which I posted only to show how to get the first idea in J.F.Sebastian's answer to work, and which like his, returned a non-indented string representation of the object. The latest updated version returns the Python object JSON formatted in isolation.

每个坐标dict的键将按照OP的注释之一以排序顺序显示，但前提是在驱动该过程的初始json.dumps()调用中指定了sort_keys=True关键字自变量，并且没有再将对象的类型一路更改为字符串.换句话说，包装"对象的实际类型现在得以保留.

The keys of each coordinate dict will appear in sorted order, as per one of the OP's comments, but only if a sort_keys=True keyword argument is specified in the initial json.dumps() call driving the process, and it no longer changes the object's type to a string along the way. In other words, the actual type of the "wrapped" object is now maintained.

我认为不了解我帖子的初衷会导致许多人反对该帖子，因此，主要是出于这个原因，我已经修复"并改进了我的答案多次.当前版本是我原始答案以及@Erik Allik在他的

I think not understanding the original intent of my post resulted in number of folks downvoting it—so, primarily for that reason, I have "fixed" and improved my answer several times. The current version is a hybrid of my original answer coupled with some of the ideas @Erik Allik used in his answer, plus useful feedback from other users shown in the comments below this answer.

以下代码在Python 2.7.16和3.7.4中似乎均能正常工作.

The following code appears to work unchanged in both Python 2.7.16 and 3.7.4.

from _ctypes import PyObj_FromPtr
import json
import re

class NoIndent(object):
    """ Value wrapper. """
    def __init__(self, value):
        self.value = value


class MyEncoder(json.JSONEncoder):
    FORMAT_SPEC = '@@{}@@'
    regex = re.compile(FORMAT_SPEC.format(r'(\d+)'))

    def __init__(self, **kwargs):
        # Save copy of any keyword argument values needed for use here.
        self.__sort_keys = kwargs.get('sort_keys', None)
        super(MyEncoder, self).__init__(**kwargs)

    def default(self, obj):
        return (self.FORMAT_SPEC.format(id(obj)) if isinstance(obj, NoIndent)
                else super(MyEncoder, self).default(obj))

    def encode(self, obj):
        format_spec = self.FORMAT_SPEC  # Local var to expedite access.
        json_repr = super(MyEncoder, self).encode(obj)  # Default JSON.

        # Replace any marked-up object ids in the JSON repr with the
        # value returned from the json.dumps() of the corresponding
        # wrapped Python object.
        for match in self.regex.finditer(json_repr):
            # see https://stackoverflow.com/a/15012814/355230
            id = int(match.group(1))
            no_indent = PyObj_FromPtr(id)
            json_obj_repr = json.dumps(no_indent.value, sort_keys=self.__sort_keys)

            # Replace the matched id string with json formatted representation
            # of the corresponding Python object.
            json_repr = json_repr.replace(
                            '"{}"'.format(format_spec.format(id)), json_obj_repr)

        return json_repr


if __name__ == '__main__':
    from string import ascii_lowercase as letters

    data_structure = {
        'layer1': {
            'layer2': {
                'layer3_1': NoIndent([{"x":1,"y":7}, {"x":0,"y":4}, {"x":5,"y":3},
                                      {"x":6,"y":9},
                                      {k: v for v, k in enumerate(letters)}]),
                'layer3_2': 'string',
                'layer3_3': NoIndent([{"x":2,"y":8,"z":3}, {"x":1,"y":5,"z":4},
                                      {"x":6,"y":9,"z":8}]),
                'layer3_4': NoIndent(list(range(20))),
            }
        }
    }

    print(json.dumps(data_structure, cls=MyEncoder, sort_keys=True, indent=2))

输出:

{
  "layer1": {
    "layer2": {
      "layer3_1": [{"x": 1, "y": 7}, {"x": 0, "y": 4}, {"x": 5, "y": 3}, {"x": 6, "y": 9}, {"a": 0, "b": 1, "c": 2, "d": 3, "e": 4, "f": 5, "g": 6, "h": 7, "i": 8, "j": 9, "k": 10, "l": 11, "m": 12, "n": 13, "o": 14, "p": 15, "q": 16, "r": 17, "s": 18, "t": 19, "u": 20, "v": 21, "w": 22, "x": 23, "y": 24, "z": 25}],
      "layer3_2": "string",
      "layer3_3": [{"x": 2, "y": 8, "z": 3}, {"x": 1, "y": 5, "z": 4}, {"x": 6, "y": 9, "z": 8}],
      "layer3_4": [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
    }
  }
}

这篇关于使用JSON模块进行漂亮打印时，如何实现自定义缩进?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！