def get_feature_type(feature_column):
    """
    For a given feature, determine if it is real, binary or constant.
    Here binary means that only two unique values occur in the feature.

    :param feature_column: The feature column
    :type feature_column: pandas.Series
    :return: 'constant', 'binary' or 'real'
    """
    n_unique_values = len(set(feature_column.values))
    if n_unique_values == 1:
        return 'constant'
    elif n_unique_values == 2:
        return 'binary'
    else:
        return 'real'
