code: def _sig_key(key, date_stamp, regionName, serviceName):
      '''
      Get a signature key. See:
  
      http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-python
      '''
      kDate = _sign(('AWS4' + key).encode('utf-8'), date_stamp)
      if regionName:
          kRegion = _sign(kDate, regionName)
          kService = _sign(kRegion, serviceName)
      else:
          kService = _sign(kDate, serviceName)
      kSigning = _sign(kService, 'aws4_request')
      return kSigninf _sig_key(key, date_stamp, regionName, serviceName):
      '''
      Get a signature key. See:
  
      http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-python
      '''
      kDate = _sign(('AWS4' + key).encode('utf-8'), date_stamp)
      if regionName:
          kRegion = _sign(kDate, regionName)
          kService = _sign(kRegion, serviceName)
      else:
          kService = _sign(kDate, serviceName)
      kSigning = _sign(kService, 'aws4_request')
      return kSigning
docs: Get a signature key. See:
  
      http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-python