How can I upload a "file" to S3 by creating a temporary file using AWS Lambda?

I am writing a lambda function whose purpose is to load a .json file from s3, change its contents, and then reload into the same bucket under a different key.

So in my s3 I have cloud cloud / folder / foo.json

>>> foo.json
{
   "value1": "abc",
   "value2": "123"
}

      

        
        
        
      

    

I want to download it, change a couple of things accordingly, and re-download it at the same location as bar.json

I have the first piece of work in which it loads the content of the file and changes the content, but now it's all a dictionary-dictionary.

import boto3
import json


def get_json():
    client = boto3.client('s3')
    response = client.get_object(Bucket='cloud', Key='folder/foo.json')
    data = response['Body'].read()
    bar = json.loads(data)
    bar["value-1"] = "do-re-mi"

    #TODO: implement uploading here   

def lambda_handler(event, context):
    get_json()
    return 'Hello from Lambda'

      

        
        
        
      

    

So now ...

>>> bar
{
   "value1": "do-re-mi",
   "value2": "123"
}

      

        
        
        
      

    

The variable bar is correct, but it is a dictionary object. How can I directly load bar.json into this bucket? I've seen other examples here, but I'm not interested in embedding my AWS secret or access keys anywhere. I am assuming that I am using lambda. I cannot create the file on the machine when I try to do something like below:

g = open('myfile.json', 'w')
g.write(json.dumps(bar, indent=4, sort_keys=True))
g.close()

with open('myfile.json', 'rb') as f:
    client.upload_fileobj(f, 'cloud', 'bar.json')

      

        
        
        
      

    

I get "errorType": "IOError", "errorMessage": "[Errno 30] Read-only filesystem: 'myfile.json'"

Any advice would be greatly appreciated. Thank!