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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 get_default_class1_models_dir(test_exists=True):
 """ Return the absolute path to the default class1 models dir. If environment variable MHCFLURRY_DEFAULT_CLASS1_MODELS is set to an absolute path, return that path. If it's set to a relative path (i.e. does not start with /) then return that path taken to be relative to the mhcflurry downloads dir. If environment variable MHCFLURRY_DEFAULT_CLASS1_MODELS is NOT set, then return the path to downloaded models in the "models_class1" download. Parameters test_exists : boolean, optional Whether to raise an exception of the path does not exist Returns ------- string : absolute path """

    if _MHCFLURRY_DEFAULT_CLASS1_MODELS_DIR:
        result = join(get_downloads_dir(), _MHCFLURRY_DEFAULT_CLASS1_MODELS_DIR)
        if test_exists and not exists(result):
            raise IOError("No such directory: %s" % result)
        return result
    else:
        return get_path("models_class1", "models", test_exists=test_exists)