nbconvert preprocessor to extract attachments

extract_attachments.py

""" A preprocessor that extracts all of the attachments from the notebook file.
The extracted attachments are returned in the 'resources' dictionary.

Based on the ExtractOutputsProcessor in nbconvert... the license for
nbconvert is

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"""

from binascii import a2b_base64
import sys
import os

from traitlets import Unicode, Set
from nbconvert.preprocessors.base import Preprocessor


class ExtractAttachmentsPreprocessor(Preprocessor):
    """
    Extracts all of the outputs from the notebook file.  The extracted
    outputs are returned in the 'resources' dictionary.
    """

    output_filename_template = Unicode(
        "attach_{cell_index}_{name}"
    ).tag(config=True)

    extract_output_types = Set(
        {'image/png', 'image/jpeg', 'image/svg+xml', 'application/pdf'}
    ).tag(config=True)

    def preprocess_cell(self, cell, resources, cell_index):
        """
        Apply a transformation on each cell,

        Parameters
        ----------
        cell : NotebookNode cell
            Notebook cell being processed
        resources : dictionary
            Additional resources used in the conversion process.  Allows
            preprocessors to pass variables into the Jinja engine.
        cell_index : int
            Index of the cell being processed (see base.py)
        """

        # Get files directory if it has been specified
        output_files_dir = resources.get('output_files_dir', None)

        # Make sure outputs key exists
        if not isinstance(resources['outputs'], dict):
            resources['outputs'] = {}

        # Loop through all of the attachments in the cell
        for name, attach in cell.get("attachments", {}).items():
            for mime, data in attach.items():
                if mime not in self.extract_output_types:
                    continue

                # Binary files are base64-encoded, SVG is already XML
                if mime in {'image/png', 'image/jpeg', 'application/pdf'}:
                    # data is b64-encoded as text (str, unicode),
                    # we want the original bytes
                    data = a2b_base64(data)
                elif sys.platform == 'win32':
                    data = data.replace('\n', '\r\n').encode("UTF-8")
                else:
                    data = data.encode("UTF-8")

                filename = self.output_filename_template.format(
                    cell_index=cell_index,
                    name=name,)

                if output_files_dir is not None:
                    filename = os.path.join(output_files_dir, filename)

                if name.endswith(".gif") and mime == "image/png":
                    filename = filename.replace(".gif", ".png")

                # In the resources, make the figure available via
                #   resources['outputs']['filename'] = data
                resources['outputs'][filename] = data

                # now we need to change the cell source so that it links to the
                # filename instead of `attachment:`
                attach_str = "attachment:"+name
                if attach_str in cell.source:
                    cell.source = cell.source.replace(attach_str, filename)

        return cell, resources

Hi

how do I direct the preprocessor to create folder with ipynb file name +_files and have the attachment files go there?