def flatten_nested_input_types(input_types):
        """Flattens nested column schema inputs into a single list."""
        if isinstance(input_types[0], list):
            input_types = [
                sub_input for input_obj in input_types for sub_input in input_obj
            ]
        return input_types
Flattens nested column schema inputs into a single list.
featuretools/primitives/base/primitive_base.py