code: def get(cls, user_agent=None, user_agent_config_yaml=None, user_agent_lookup=None, **kwargs):
          # type: (Optional[str], Optional[str], Optional[str], Any) -> str
          
          if user_agent or user_agent_config_yaml or 'user_agent' in UserAgent._environment_variables(**kwargs):
              return UserAgent._create(user_agent, user_agent_config_yaml, user_agent_lookup, **kwargs)
          if cls.user_agent:
              return cls.user_agent
          else:
              raise UserAgentError(
                  'You must either set the global user agent: UserAgent.set_global(...) or pass in user agent parameters!')
docs: Get full user agent string from parameters if supplied falling back on global user agent if set.
  
          Args:
              user_agent (Optional[str]): User agent string. HDXPythonLibrary/X.X.X- is prefixed.
              user_agent_config_yaml (Optional[str]): Path to YAML user agent configuration. Ignored if user_agent supplied. Defaults to ~/.useragent.yml.
              user_agent_lookup (Optional[str]): Lookup key for YAML. Ignored if user_agent supplied.
  
          Returns:
              str: Full user agent string