def _build_projection_expression(clean_table_keys):
    """Given cleaned up keys, this will return a projection expression for
    the dynamodb lookup.

    Args:
        clean_table_keys (dict): keys without the data types attached

    Returns:
        str: A projection expression for the dynamodb lookup.
    """
    projection_expression = ''
    for key in clean_table_keys[:-1]:
        projection_expression += ('{},').format(key)
    projection_expression += clean_table_keys[-1]
    return projection_expression
Given cleaned up keys, this will return a projection expression for
    the dynamodb lookup.

    Args:
        clean_table_keys (dict): keys without the data types attached

    Returns:
        str: A projection expression for the dynamodb lookup.