問題描述

我在 python 2.6 中使用標準 json 模塊 來序列化浮點列表.但是，我得到這樣的結果:

I am using the standard json module in python 2.6 to serialize a list of floats. However, I'm getting results like this:

>>> import json
>>> json.dumps([23.67, 23.97, 23.87])
'[23.670000000000002, 23.969999999999999, 23.870000000000001]'

我希望浮點數的格式只有兩位小數.輸出應如下所示:

I want the floats to be formated with only two decimal digits. The output should look like this:

>>> json.dumps([23.67, 23.97, 23.87])
'[23.67, 23.97, 23.87]'

我嘗試定義自己的 JSON 編碼器類:

I have tried defining my own JSON Encoder class:

class MyEncoder(json.JSONEncoder):
    def encode(self, obj):
        if isinstance(obj, float):
            return format(obj, '.2f')
        return json.JSONEncoder.encode(self, obj)

這適用于唯一的浮動對象:

This works for a sole float object:

>>> json.dumps(23.67, cls=MyEncoder)
'23.67'

但嵌套對象失敗:

>>> json.dumps([23.67, 23.97, 23.87])
'[23.670000000000002, 23.969999999999999, 23.870000000000001]'

我不想有外部依賴，所以我更喜歡堅持使用標準的 json 模塊.

I don't want to have external dependencies, so I prefer to stick with the standard json module.

我怎樣才能做到這一點?

How can I achieve this?

推薦答案

注意:這不在任何最新版本的 Python 中都有效.

Note: This does not work in any recent version of Python.

不幸的是，我認為您必須通過猴子修補來做到這一點(在我看來，這表明標準庫 json 包中的設計缺陷).例如，這段代碼:

Unfortunately, I believe you have to do this by monkey-patching (which, to my opinion, indicates a design defect in the standard library json package). E.g., this code:

import json
from json import encoder
encoder.FLOAT_REPR = lambda o: format(o, '.2f')
    
print(json.dumps(23.67))
print(json.dumps([23.67, 23.97, 23.87]))

發射:

23.67
[23.67, 23.97, 23.87]

如你所愿.顯然，應該有一種架構化的方式來覆蓋 FLOAT_REPR ，這樣如果你愿意，浮點的每一個表示都在你的控制之下；但不幸的是，這不是 json 包的設計方式:-(.

as you desire. Obviously, there should be an architected way to override FLOAT_REPR so that EVERY representation of a float is under your control if you wish it to be; but unfortunately that's not how the json package was designed:-(.

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