def parse_methods(csv_file, errors_dict):
    """
    Parses the input CSV file with columns (method, usability, errors)
    and yields `MethodInfo` instances as a result.
    """
    with csv_file.open(newline='') as f:
        f = csv.reader(f)
        next(f, None)  # header
        for line, (method, usability, errors) in enumerate(f, start=2):
            try:
                errors = [errors_dict[x] for x in errors.split()]
            except KeyError:
                raise ValueError('Method {} references unknown errors {}'
                                 .format(method, errors)) from None

            yield MethodInfo(method, usability, errors)