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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 _parse_variable_defaults(cls, defaults):
 """Parse out all of the variable defaults."""


        default_dict = {}

        for item in defaults:
            key = next(iter(item))
            value = item[key]

            if key in default_dict:
                raise RecipeFileInvalid("Default variable value specified twice", name=key, old_value=default_dict[key], new_value=value)

            default_dict[key] = value

        return default_dict