python - How to encode bytes in JSON? json.dumps() throwing a TypeError

Question

I am trying to encode a dictionary containing a string of bytes with json, and getting a is not JSON serializable error:

import base64
import json

data = {}
encoded = base64.b64encode(b'data to be encoded')
data['bytes'] = encoded

print(json.dumps(data))

The error I get:

TypeError: b'ZGF0YSB0byBiZSBlbmNvZGVk
' is not JSON serializable

How can I correctly encode my dictionary containing bytes with JSON?

Answer 1

The JSON format only supports unicode strings. Since base64.b64encode encodes bytes to ASCII-only bytes, you can use that codec to decode the data:

import base64

encoded = base64.b64encode(b'data to be encoded')  # b'ZGF0YSB0byBiZSBlbmNvZGVk' (notice the "b")
data['bytes'] = encoded.decode('ascii')            # 'ZGF0YSB0byBiZSBlbmNvZGVk'

Note that to get the original data back you don't need to re-encode it to bytes because b64decode handles ASCII-only strings as well as bytes:

decoded = base64.b64decode(data['bytes'])  # b'data to be encoded'