将二维列表写入JSON文件

我有一个二维列表，例如：

data = [[1,2,3], [2,3,4], [4,5,6]]

我想将其写入 JSON 文件，如下所示：

{
    'data':[
        [1,2,3],
        [2,3,4],
        [4,5,6]
    ]
}

我得到这个：json.dumps(data, indent=4, sort_keys=True):

{
    'data':[
        [
         1,
         2,
         3
        ],
        [
         2,
         3,
         4
        ],
        [
         4,
         5,
         6]
    ]
}

这是另一个问题使用 JSON 模块进行漂亮打印时如何实现自定义缩进？ https://stackoverflow.com/questions/13249415/how-to-implement-custom-indentation-when-pretty-printing-with-the-json-module，但那是字典。

我以为你可以用我的答案 https://stackoverflow.com/a/13252112/355230到另一个类似的问题来做你想做的事。虽然它与json.dumps()，你指出由于某种原因它没有json.dump().

调查此事后，我发现encode()的推导方法json.JSONEncoder链接答案中被覆盖的类仅在以下情况下调用dumps()被调用，但不是在什么时候调用dump()叫做。

幸运的是，我能够确定iterencode() method does在这两种情况下都会被调用 - 因此能够通过或多或少简单地将代码从encode() to iterencode().

下面的代码是修改后的版本，其中包含以下更改：

Modified我对其他问题的回答中的代码版本：

from _ctypes import PyObj_FromPtr  # see https://stackoverflow.com/a/15012814/355230
import json
import re


class NoIndent(object):
    """ Value wrapper. """
    def __init__(self, value):
        if not isinstance(value, (list, tuple)):
            raise TypeError('Only lists and tuples can be wrapped')
        self.value = value


class MyEncoder(json.JSONEncoder):
    FORMAT_SPEC = '@@{}@@'  # Unique string pattern of NoIndent object ids.
    regex = re.compile(FORMAT_SPEC.format(r'(\d+)'))  # compile(r'@@(\d+)@@')

    def __init__(self, **kwargs):
        # Keyword arguments to ignore when encoding NoIndent wrapped values.
        ignore = {'cls', 'indent'}

        # Save copy of any keyword argument values needed for use here.
        self._kwargs = {k: v for k, v in kwargs.items() if k not in ignore}
        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 iterencode(self, obj, **kwargs):
        format_spec = self.FORMAT_SPEC  # Local var to expedite access.

        # Replace any marked-up NoIndent wrapped values in the JSON repr
        # with the json.dumps() of the corresponding wrapped Python object.
        for encoded in super(MyEncoder, self).iterencode(obj, **kwargs):
            match = self.regex.search(encoded)
            if match:
                id = int(match.group(1))
                no_indent = PyObj_FromPtr(id)
                json_repr = json.dumps(no_indent.value, **self._kwargs)
                # Replace the matched id string with json formatted representation
                # of the corresponding Python object.
                encoded = encoded.replace(
                            '"{}"'.format(format_spec.format(id)), json_repr)

            yield encoded

将其应用于您的问题：

# Example of using it to do get the results you want.

alfa = [('a','b','c'), ('d','e','f'), ('g','h','i')]
data = [(1,2,3), (2,3,4), (4,5,6)]

data_struct = {
    'data': [NoIndent(elem) for elem in data],
    'alfa': [NoIndent(elem) for elem in alfa],
}

print(json.dumps(data_struct, cls=MyEncoder, sort_keys=True, indent=4))

# Test custom JSONEncoder with json.dump()
with open('data_struct.json', 'w') as fp:
    json.dump(data_struct, fp, cls=MyEncoder, sort_keys=True, indent=4)
    fp.write('\n')  # Add a newline to very end (optional).

结果输出：

{
    "alfa": [
        ["a", "b", "c"],
        ["d", "e", "f"],
        ["g", "h", "i"]
    ],
    "data": [
        [1, 2, 3],
        [2, 3, 4],
        [4, 5, 6]
    ]
}