code: def from_environment_variables(cls):
          
          ip = os.environ.get('ONEVIEWSDK_IP', '')
          image_streamer_ip = os.environ.get('ONEVIEWSDK_IMAGE_STREAMER_IP', '')
          api_version = int(os.environ.get('ONEVIEWSDK_API_VERSION', OneViewClient.DEFAULT_API_VERSION))
          ssl_certificate = os.environ.get('ONEVIEWSDK_SSL_CERTIFICATE', '')
          username = os.environ.get('ONEVIEWSDK_USERNAME', '')
          auth_login_domain = os.environ.get('ONEVIEWSDK_AUTH_LOGIN_DOMAIN', '')
          password = os.environ.get('ONEVIEWSDK_PASSWORD', '')
          proxy = os.environ.get('ONEVIEWSDK_PROXY', '')
          sessionID = os.environ.get('ONEVIEWSDK_SESSIONID', '')
          timeout = os.environ.get('ONEVIEWSDK_CONNECTION_TIMEOUT')
  
          config = dict(ip=ip,
                        image_streamer_ip=image_streamer_ip,
                        api_version=api_version,
                        ssl_certificate=ssl_certificate,
                        credentials=dict(userName=username, authLoginDomain=auth_login_domain, password=password, sessionID=sessionID),
                        proxy=proxy, timeout=timeout)
  
          return cls(config)
docs: Construct OneViewClient using environment variables.
  
          Allowed variables: ONEVIEWSDK_IP (required), ONEVIEWSDK_USERNAME (required), ONEVIEWSDK_PASSWORD (required),
          ONEVIEWSDK_AUTH_LOGIN_DOMAIN, ONEVIEWSDK_API_VERSION, ONEVIEWSDK_IMAGE_STREAMER_IP, ONEVIEWSDK_SESSIONID, ONEVIEWSDK_SSL_CERTIFICATE,
          ONEVIEWSDK_CONNECTION_TIMEOUT and ONEVIEWSDK_PROXY.
  
          Returns:
              OneViewClient: