In Python 3.x you need to convert your str object to a bytes object for base64 to be able to encode them. You can do that using the str.encode method:

>>> import json
>>> import base64
>>> d = {"alg": "ES256"} 
>>> s = json.dumps(d)  # Turns your json dict into a str
>>> print(s)
{"alg": "ES256"}
>>> type(s)
<class 'str'>
>>> base64.b64encode(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.2/base64.py", line 56, in b64encode
    raise TypeError("expected bytes, not %s" % s.__class__.__name__)
TypeError: expected bytes, not str
>>> base64.b64encode(s.encode('utf-8'))
b'eyJhbGciOiAiRVMyNTYifQ=='

If you pass the output of your_str_object.encode('utf-8') to the base64 module, you should be able to encode it fine.

Considering that you have loaded the json data into an object. You can then try the following:

import json
import base64

json_obj = {
    "equno": "229151246954324320",
    "data": "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"
}

print(base64.b64decode(json_obj["data"]))

resp = requests.get(url, headers=headers, json=json, timeout=6)

getmetadata = resp.json()['objects'][1]['metadata']
newdata = base64.b64decode(getmetadata).decode('UTF-8')
data = json.loads(newdata)
print(data['complete'])

base64.b64decode(str).decode(str) returns a string str. If that string should be json then you can use json.loads to transform the string str to a dict where you can get a single value by it's key.

You can also do in JavaScript

    btoa(unescape(encodeURIComponent(JSON.stringify({"é": "è"}))))
    base64 output: eyLDqSI6IsOoIn0=

though I think btoa works on just the extended ascii table, not all unicode characters.

Then in Python

    json.loads(base64.b64decode("eyLDqSI6IsOoIn0=")
    prints: {'é': 'è'}

You are passing in your whole list, which itself contains more lists:

>>> response_i['objcontent'][0]['rowvalues']
[['AAAAAAAALkA=', 'AAAAAADgU8A=', 'AAAAAAAA8D8=', '7HitYA'], ['AAAAAAAALkA=', 'AAAAAADgU8A=', 'AAAAAAAACEA=', '7HitYA'], ['AAAAAAAALkA=', 'AAAAAADgU8A=', 'AAAAAAAAFEA=', '7HitYA']]

You'd need to decode each separate entry, not the whole list:

for response_i in response['response']:
    for row in response_i['objcontent'][0]['rowvalues']:
        for encoded_obj in row[:-1]:
            decoded = base64.b64decode(encoded_obj)

Note that I ignore the last value in the row, that's not a Base64 value.

Your next problem is that your Base64 data doesn't contain enough bytes to hold 12 float values (each 8 bytes, so you'd need 96 bytes). Since they are 8 bytes each, you probably have just one floating point value in each string.

So you'd want to decode just the one float:

floating_point_value = struct.unpack('d', decoded)[0]

Demo:

>>> for response_i in response['response']:
...     for row in response_i['objcontent'][0]['rowvalues']:
...         for encoded_obj in row[:-1]:
...             decoded = base64.b64decode(encoded_obj)
...             print(struct.unpack('d', decoded)[0])
...
15.0
-79.5
1.0
15.0
-79.5
3.0
15.0
-79.5
5.0

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)

Thank you all for your help.

After lots of searching on Stackoverflow coupled with testing on my local machine I was able to drill it down to this.

The object (a['data']) that was being passed in had some values that were not utf-8 decodable.

It was in the form of b'xxxsknoen'

I ended up deleting the b and the quotes in the front and end and then converting it to an str.

var = base64.b64decode(str(a['data'])[2:-1]).decode('utf-8')
a.update(json.loads(var))

base64.b64encode(data) will output an object in bytes

encoded = base64.b64encode(data).decode() converts it to string

after that you might need (quite common) to do url encoding to the string

from urllib.parse import urlencode
urlencode({"groupedImage": encoded})