return value of python AWS Lambda.

Question

I am trying to read dynamodb table and return values in python of Lambda. My return function is below

return {
                'statusCode': 200,
                # 'headers': {
                #     'Access-Control-Allow-Headers': 'Content-Type',
                #     'Access-Control-Allow-Origin': '*',
                #     'Access-Control-Allow-Methods': 'OPTIONS,GET'
                #     },
                'body': json.dumps(table.scan()['Items'][0])
            }

The problem is json.dumps(). Normally, I use table.scan()['Items'] as the value, and it applied 3 tables. Two tables work well but one table doesn't. If I use table.scan()['Items'][0], it works. However, I would like to whole table values.

Answer

Decimal object is not JSON serializable. Use a package that can do that for you [1] or consider casting the Decimal into a float using a helper function [2].

1. Use [`simplejson`](https://github.com/simplejson/simplejson) instead of `json` as it will do the decimal conversion for you. This would mean you need to use a [Lambda layer](https://docs.aws.amazon.com/lambda/latest/dg/configuration-layers.html) to import that pip package.

`import simplejson as json`

2. Use a custom class to do the conversion meaning you can avoid the Lambda layer:

```
from decimal import Decimal

class DecimalEncoder(json.JSONEncoder):
  def default(self, obj):
    if isinstance(obj, Decimal):
      return str(obj)
    return json.JSONEncoder.default(self, obj)
```
```
json.dumps(item, cls=DecimalEncoder)
```

Answer

When you say "one table doesn't work" could you provide more information? Such as an error message? Or what you're expecting.

As I understand it, `table.scan()` only scans a single table so I'm not sure what is meant by "it applied 3 tables".

Running `json.dumps(table.scan()['Items'])` will return all of the items in the table. Running `json.dumps(table.scan()['Items'][0])` will return the first element of the list.

Answer

My code is

def lambda_handler(event, context): dynamodb = boto3.resource("dynamodb") table = dynamodb.Table("OrderList") items = table.scan()['Items'] return { 'statusCode': 200, 'body': json.dumps(items[1]) }

Response is { "statusCode": 200, "body": "{"TotalPrice": "101", "PartName": "Test Part", "ClientID": "user001", "UnitPrice": "50", "OrderDate": "28-10-2022", "PartID": "P003", "Status": "Sent", "Quantity": "1", "OrderID": "O0001"}" }

################################### return { 'statusCode': 200, 'body': json.dumps(items[1]) }

Response is { "errorMessage": "Object of type Decimal is not JSON serializable", "errorType": "TypeError", "requestId": "5849b770-4dc6-4858-82ed-65fbecab1f6a", "stackTrace": [ " File "/var/task/lambda_function.py", line 76, in lambda_handler
 'body': json.dumps(items)
", " File "/var/lang/lib/python3.9/json/init.py", line 231, in dumps
 return _default_encoder.encode(obj)
", " File "/var/lang/lib/python3.9/json/encoder.py", line 199, in encode
 chunks = self.iterencode(o, _one_shot=True)
", " File "/var/lang/lib/python3.9/json/encoder.py", line 257, in iterencode
 return _iterencode(o, 0)
", " File "/var/lang/lib/python3.9/json/encoder.py", line 179, in default
 raise TypeError(f'Object of type {o.class.name} '
" ] }

return value of python AWS Lambda.

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