def transform_schema(schema, transform_spec):
    """Creates a post-transform given a pre-transform schema and a transform_spec with mutation instructions.

    :param schema: A pre-transform schema
    :param transform_spec: a TransformSpec object with mutation instructions.
    :return: A post-transform schema
    """
    removed_fields = set(transform_spec.removed_fields)
    unknown_field_names = removed_fields - set(schema.fields.keys())
    if unknown_field_names:
        warnings.warn('remove_fields specified some field names that are not part of the schema. '
                      'These field names will be ignored "{}". '.format(', '.join(unknown_field_names)))

    exclude_fields = {f[0] for f in transform_spec.edit_fields} | removed_fields
    fields = [v for k, v in schema.fields.items() if k not in exclude_fields]

    for field_to_edit in transform_spec.edit_fields:
        edited_unischema_field = UnischemaField(name=field_to_edit[0], numpy_dtype=field_to_edit[1],
                                                shape=field_to_edit[2], codec=None, nullable=field_to_edit[3])
        fields.append(edited_unischema_field)

    if transform_spec.selected_fields is not None:
        unknown_field_names = set(transform_spec.selected_fields) - set(f.name for f in fields)
        if unknown_field_names:
            warnings.warn('selected_fields specified some field names that are not part of the schema. '
                          'These field names will be ignored "{}". '.format(', '.join(unknown_field_names)))
        fields = [f for f in fields if f.name in transform_spec.selected_fields]
        fields = sorted(fields, key=lambda f: transform_spec.selected_fields.index(f.name))

    return Unischema(schema._name + '_transformed', fields)
Creates a post-transform given a pre-transform schema and a transform_spec with mutation instructions.

    :param schema: A pre-transform schema
    :param transform_spec: a TransformSpec object with mutation instructions.
    :return: A post-transform schema
    
petastorm/transform.py