boto3 s3 connection error: An error occurred (SignatureDoesNotMatch) when calling the ListBuckets operation - python-3.x

Question

I'm using the boto3 package to connect from outside an s3 cluster (i.e. the script is currently not being run within the AWS 'cloud', but from my MBP connecting to the relevant cluster). My code:
s3 = boto3.resource(
"s3",
aws_access_key_id=self.settings['CREDENTIALS']['aws_access_key_id'],
aws_secret_access_key=self.settings['CREDENTIALS']['aws_secret_access_key'],
)
bucket = s3.Bucket(self.settings['S3']['bucket_test'])
for bucket_in_all in boto3.resource('s3').buckets.all():
if bucket_in_all.name == self.settings['S3']['bucket_test']:
print ("Bucket {} verified".format(self.settings['S3']['bucket_test']))
Now I'm receiving this error message:
botocore.exceptions.ClientError: An error occurred (SignatureDoesNotMatch) when calling the ListBuckets operation
I'm aware of the sequence of how the aws credentials are checked, and tried different permutations of my environment variables and ~/.aws/credentials, and know that the credentials as per my .py script should override, however I'm still seeing this SignatureDoesNotMatch error message. Any ideas where I may be going wrong? I've also tried:
# Create a session
session = boto3.session.Session(
aws_access_key_id=self.settings['CREDENTIALS']['aws_access_key_id'],
aws_secret_access_key=self.settings['CREDENTIALS']['aws_secret_access_key'],
aws_session_token=self.settings['CREDENTIALS']['session_token'],
region_name=self.settings['CREDENTIALS']['region_name']
)
s3 = boto3.resource('s3')
for bucket in s3.buckets.all():
print(bucket.name)
...however I also see the same error traceback.

Answer 1

Actually, this was partly answered by #John Rotenstein and #bdcloud nevertheless I need to be more specific...
The following code in my case was not necessary and causing the error message:
# Create a session
session = boto3.session.Session(
aws_access_key_id=self.settings['CREDENTIALS']['aws_access_key_id'],
aws_secret_access_key=self.settings['CREDENTIALS']['aws_secret_access_key'],
aws_session_token=self.settings['CREDENTIALS']['session_token'],
region_name=self.settings['CREDENTIALS']['region_name']
)
The credentials now stored in self.settings mirror the ~/.aws/credentials. Weirdly (and like last week where the reverse happened), I now have access. It could be that a simple reboot of my laptop meant that my new credentials (since I updated these again yesterday) in ~/.aws/credentials were then 'accepted'.