title: python default configuration reuse of variables
body: <pre><code>class DefaultConfig(object):
      class S3(object):
          DATA_ROOT = 's3://%(bucket_name)s/NAS'
          DATA_LOCATION = '{}/%(instrument_id)s/%(run_id)s'.format(DefaultConfig.S3.DATA_ROOT)
  </code></pre>
  
  <p>The code above gives me the following error. </p>
  
  <pre><code>      File "./s3Utils.py", line 5, in &lt;module&gt;
      from InfraConfig import InfraConfig as IC
    File "/opt/src/datasource/src/main/python/util/InfraConfig.py", line 4, in &lt;module&gt;
      class DefaultConfig(object):
    File "/opt/src/datasource/src/main/python/util/InfraConfig.py", line 6, in DefaultConfig
      class S3(object):
    File "/opt/src/datasource/src/main/python/util/InfraConfig.py", line 14, in S3
      DATA_LOCATION = '{}/%(instrument_id)s/%(run_id)s'.format(DefaultConfig.S3.DATA_ROOT)
  NameError: name 'DefaultConfig' is not defined
  </code></pre>
  
  <p>Why is it unable to find DefaultConfig.S3.DATA_ROOT
  Also, this is my attempt at writing structured configuration with reuse of values of DefaultConfig. Is there a way to do this without writing a yml file?</p>