在 JSON 中序列化一个 base64 编码的数据

Question

我正在编写一个脚本来为演示自动生成数据，我需要在 JSON 中序列化一些数据。此数据的一部分是图像，因此我将其编码为 base64，但是当我尝试运行我的脚本时，我得到：

Traceback (most recent call last):
  File "lazyAutomationScript.py", line 113, in <module>
    json.dump(out_dict, outfile)
  File "/usr/lib/python3.4/json/__init__.py", line 178, in dump
    for chunk in iterable:
  File "/usr/lib/python3.4/json/encoder.py", line 422, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/usr/lib/python3.4/json/encoder.py", line 396, in _iterencode_dict
    yield from chunks
  File "/usr/lib/python3.4/json/encoder.py", line 396, in _iterencode_dict
    yield from chunks
  File "/usr/lib/python3.4/json/encoder.py", line 429, in _iterencode
    o = _default(o)
  File "/usr/lib/python3.4/json/encoder.py", line 173, in default
    raise TypeError(repr(o) + " is not JSON serializable")
  TypeError: b'iVBORw0KGgoAAAANSUhEUgAADWcAABRACAYAAABf7ZytAAAABGdB...
     ...
   BF2jhLaJNmRwAAAAAElFTkSuQmCC' is not JSON serializable

据我所知，base64 编码的任何东西（在本例中为 PNG 图像）只是一个字符串，因此它应该会给序列化带来问题。我错过了什么？

Answer 1

您必须注意数据类型。

如果你读取二进制图像，你会得到字节。如果你用 base64 对这些字节进行编码，你又会得到 ... 字节！（请参阅有关 b64encode 的文档）

json 无法处理原始字节，这就是您收到错误的原因。

刚刚写了一些例子，附上注释，希望对你有帮助：

from base64 import b64encode
from json import dumps

ENCODING = 'utf-8'
IMAGE_NAME = 'spam.jpg'
JSON_NAME = 'output.json'

# first: reading the binary stuff
# note the 'rb' flag
# result: bytes
with open(IMAGE_NAME, 'rb') as open_file:
    byte_content = open_file.read()

# second: base64 encode read data
# result: bytes (again)
base64_bytes = b64encode(byte_content)

# third: decode these bytes to text
# result: string (in utf-8)
base64_string = base64_bytes.decode(ENCODING)

# optional: doing stuff with the data
# result here: some dict
raw_data = {IMAGE_NAME: base64_string}

# now: encoding the data to json
# result: string
json_data = dumps(raw_data, indent=2)

# finally: writing the json string to disk
# note the 'w' flag, no 'b' needed as we deal with text here
with open(JSON_NAME, 'w') as another_open_file:
    another_open_file.write(json_data)

Answer 2

替代解决方案是使用自定义编码器动态编码内容：

import json
from base64 import b64encode

class Base64Encoder(json.JSONEncoder):
    # pylint: disable=method-hidden
    def default(self, o):
        if isinstance(o, bytes):
            return b64encode(o).decode()
        return json.JSONEncoder.default(self, o)

有了这个定义你可以做：

m = {'key': b'\x9c\x13\xff\x00'}
json.dumps(m, cls=Base64Encoder)

它将产生：

'{"key": "nBP/AA=="}'

Answer 3

What am I missing?

错误是 binary 不可 JSON 序列化。

from base64 import b64encode

# *binary representation* of the base64 string
assert b64encode(b"binary content")                 == b'YmluYXJ5IGNvbnRlbnQ='

# base64 string
assert b64encode(b"binary content").decode('utf-8') ==  'YmluYXJ5IGNvbnRlbnQ='

后者肯定是 "JSON serializable" 因为是二进制 b"binary content".

的 base64 字符串表示

在 JSON 中序列化一个 base64 编码的数据

Serialize in JSON a base64 encoded data

base64

serialization

json

python-3.x