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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _create(cls, user_agent=None, user_agent_config_yaml=None, user_agent_lookup=None, **kwargs):
 # type: (Optional[str], Optional[str], Optional[str], Any) -> str """ Get full user agent string 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 """

        kwargs = UserAgent._environment_variables(**kwargs)
        if 'user_agent' in kwargs:
            user_agent = kwargs['user_agent']
            del kwargs['user_agent']
        prefix = kwargs.get('prefix')
        if prefix:
            del kwargs['prefix']
        else:
            prefix = 'HDXPythonUtilities/%s' % get_utils_version()
        if not user_agent:
            ua = cls._load(prefix, user_agent_config_yaml, user_agent_lookup)
        else:
            ua = cls._construct(kwargs, prefix, user_agent)
        return ua