Read Binary string in Python, zlib

Question

I want to store a large JSON (dict) from Python in dynamoDB.

After some investigation it seems that zlib is the way to go to get compression at a good level. Using below Im able to encode the dict.

ranking_compressed = zlib.compress(simplejson.dumps(response["Item"]["ranking"]).encode('utf-8'))

The (string?) then looks like this: b'x\x9c\xc5Z\xdfo\xd3....

I can directly decompress this and get the dict back with:

ranking_decompressed = simplejson.loads(str(zlib.decompress(ranking_compressed).decode('utf-8')))

All good so far. However, when putting this in dynamoDB and then reading it back using the same decompress code as above. The (string?) now looks like this:

Binary(b'x\x9c\xc5Z\xdf...

The error I get is:

 bytes-like object is required, not 'Binary'

Ive tried accessing the Binary with e.g. .data but I cant reach it.

Any help is appreciated.

Try if you can access the content of the Binary obnect with .value. — Klaus D.
– Klaus D., Commented Jan 31, 2017 at 0:43
@KlausD. Thanks! That did the trick :). Write an answer and Ill accept it! — KalleJuhans
– KalleJuhans, Commented Jan 31, 2017 at 20:38

GreenMachine · Accepted Answer · 2019-05-17 02:01:17Z

2

Boto3 Binary objects have a value property.

# in general...
binary_obj.value
# for your specific case...
ranking_decompressed = simplejson.loads(str(zlib.decompress(response["Item"]["ranking_compressed"].value).decode('utf-8')))

Oddly, this seems to be documented nowhere except the source code for the Binary class here

edited May 17, 2019 at 2:01

answered May 17, 2019 at 1:53

GreenMachine

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