I can't reproduce it:
File "test1.py", line 19, in do_get_obj
response = s3_client.get_object(Bucket='archpi.dabase.com', Key='style.css')
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/client.py", line 314, in _api_call
return self._make_api_call(operation_name, kwargs)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/client.py", line 599, in _make_api_call
operation_model, request_dict)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/endpoint.py", line 148, in make_request
return self._send_request(request_dict, operation_model)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/endpoint.py", line 173, in _send_request
request = self.create_request(request_dict, operation_model)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/endpoint.py", line 157, in create_request
operation_name=operation_model.name)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/hooks.py", line 227, in emit
return self._emit(event_name, kwargs)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/hooks.py", line 210, in _emit
response = handler(**kwargs)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/signers.py", line 90, in handler
return self.sign(operation_name, request)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/signers.py", line 156, in sign
auth.add_auth(request)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/auth.py", line 420, in add_auth
super(S3SigV4Auth, self).add_auth(request)
File "/Users/inada-n/tmp/boto-leak/venv/lib/python3.6/site-packages/botocore/auth.py", line 352, in add_auth
raise NoCredentialsError
botocore.exceptions.NoCredentialsError: Unable to locate credentials