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Convert Float to Decimal Data Types for Boto3 DynamoDB using Python


A quick post on a workaround when you need to convert float to decimal types.

One thing I really don't like about the AWS SDK for Python, specifically aimed towards DynamoDB is that Float types are not supported and that you should use Decimal types instead.

For example, my payload below:

>>> data
{'attempts': 5, 'min': 180.87, 'timestamp': '2019-02-05T15:48:27', 'address': '', 'max': 747.17, 'region': 'eu-west-1_dynamodb', 'avg': 311.32599999999996, 'port': 443, 'regionTo': 'us-east-1', 'results': [{'seq': 1, 'time': '747.17'}, {'seq': 2, 'time': '215.60'}, {'seq': 3, 'time': '230.67'}, {'seq': 4, 'time': '180.87'}, {'seq': 5, 'time': '182.32'}]}

Trying to write that as an Item to my DynamoDB table and you will be faced with the exception below:

>>> ddb.put_item(Item=data)
TypeError: Float types are not supported. Use Decimal types instead.

One way around this is to use parse_float in json.loads():

>>> from decimal import Decimal
>>> import json
>>> ddb_data = json.loads(json.dumps(data), parse_float=Decimal)
>>> ddb_data
{u'max': Decimal('747.17'), u'min': Decimal('180.87'), u'timestamp': u'2019-02-05T15:48:27', u'region': u'eu-west-1_dynamodb', u'regionTo': u'us-east-1', u'results': [{u'seq': 1, u'time': u'747.17'}, {u'seq': 2, u'time': u'215.60'}, {u'seq': 3, u'time': u'230.67'}, {u'seq': 4, u'time': u'180.87'}, {u'seq': 5, u'time': u'182.32'}], u'attempts': 5, u'address': u'', u'avg': Decimal('311.32599999999996'), u'port': 443}

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