S3 upload and copy with encryption

s3.py

#!/usr/bin/env python

import boto3

from boto3.s3.transfer import S3Transfer

filename = 'file.txt'
bucket_name = 'ravenskill'

s3 = boto3.resource('s3')
client = s3.meta.client

transfer = S3Transfer(client)
transfer.upload_file(filename,
                     bucket_name,
                     filename,
                     extra_args={'ServerSideEncryption': 'AES256'})

copy_source = {
    'Bucket': bucket_name,
    'Key': filename
}

bucket = s3.Bucket(bucket_name)
obj = bucket.Object(filename)
obj.copy(copy_source,
         ExtraArgs={'ServerSideEncryption': 'AES256'})

I am getting below error
NoCredentialsError: Unable to locate credentials
Do we not pass AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY values ?

You don't need to pass AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY values.
Have a look at https://boto3.amazonaws.com/v1/documentation/api/latest/guide/quickstart.html#configuration