Serialize in JSON a base64 encoded data

Question

I'm writing a script to automate data generation for a demo and I need to serialize in a JSON some data. Part of this data is an image, so I encoded it in base64, but when I try to run my script I get:

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 

As far as I know, a base64-encoded-whatever (a PNG image, in this case) is just a string, so it should pose to problem to serializating. What am I missing?

Answer 1

You must be careful about the datatypes.

If you read a binary image, you get bytes. If you encode these bytes in base64, you get ... bytes again! (see documentation on b64encode)

json can't handle raw bytes, that's why you get the error.

I have just written some example, with comments, I hope it helps:

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)