How to make multi-file upload widget in Ipython Notebook?

Question

I would like to make a widget in Ipython Notebook 3.x or 4.x (Jupyter, Python 3) for remote file upload which allows a user to select multiple files in the browser's file picker when uploading. Unfortunatelly, I have no clue about the javascript side.

I have found blueimp's widgets, however, I have no idea how to use them inside a notebook.

This is how a single file upload widget is made:

import base64
from __future__ import print_function # py 2.7 compat.
from IPython.html import widgets # Widget definitions.
from IPython.utils.traitlets import Unicode # Traitlet needed to add synced attributes to the widget.

class FileWidget(widgets.DOMWidget):
    _view_name = Unicode('FilePickerView', sync=True)
    value = Unicode(sync=True)
    filename = Unicode(sync=True)

    def __init__(self, **kwargs):
        """Constructor"""
        widgets.DOMWidget.__init__(self, **kwargs) # Call the base.

        # Allow the user to register error callbacks with the following signatures:
        #    callback()
        #    callback(sender)
        self.errors = widgets.CallbackDispatcher(accepted_nargs=[0, 1])

        # Listen for custom msgs
        self.on_msg(self._handle_custom_msg)

    def _handle_custom_msg(self, content):
        """Handle a msg from the front-end.

        Parameters
        ----------
        content: dict
            Content of the msg."""
        if 'event' in content and content['event'] == 'error':
            self.errors()
            self.errors(self)

%%javascript

require(["widgets/js/widget", "widgets/js/manager"], function(widget, manager){

    var FilePickerView = widget.DOMWidgetView.extend({
        render: function(){
            // Render the view.
            this.setElement($('<input />')
                .attr('type', 'file'));
        },

        events: {
            // List of events and their handlers.
            'change': 'handle_file_change',
        },

        handle_file_change: function(evt) { 
            // Handle when the user has changed the file.

            // Retrieve the first (and only!) File from the FileList object
            var file = evt.target.files[0];
            if (file) {

                // Read the file's textual content and set value to those contents.
                var that = this;
                var file_reader = new FileReader();
                file_reader.onload = function(e) {
                    that.model.set('value', e.target.result);
                    that.touch();
                }
                file_reader.readAsText(file);
            } else {

                // The file couldn't be opened.  Send an error msg to the
                // back-end.
                this.send({ 'event': 'error' });
            }

            // Set the filename of the file.
            this.model.set('filename', file.name);
            this.touch();
        },
    });

    // Register the FilePickerView with the widget manager.
    manager.WidgetManager.register_widget_view('FilePickerView', FilePickerView);
});

file_widget = FileWidget()

# Register an event to echo the filename when it has been changed.
def file_loading():
    print("Loading %s" % file_widget.filename)
file_widget.on_trait_change(file_loading, 'filename')

# Register an event to echo the filename and contents when a file
# has been uploaded.
def file_loaded():
    print("Loaded, file contents: %s" % file_widget.value)
file_widget.on_trait_change(file_loaded, 'value')

# Register an event to print an error message when a file could not
# be opened.  Since the error messages are not handled through
# traitlets but instead handled through custom msgs, the registration
# of the handler is different than the two examples above.  Instead
# the API provided by the CallbackDispatcher must be used.
def file_failed():
    print("Could not load file contents of %s" % file_widget.filename)
file_widget.errors.register_callback(file_failed)

file_widget

Answer 1

Comments, suggestions and fixes are welcome.

I got inspiration from Jupyter Notebook (4.x) itself from the NotebookList.prototype.handleFilesUpload function of the notebooklist.js file. After reading up on some javascript syntax, I came up with the following:

(Please note that files are uploaded in text mode without checking.)

import base64 # You need it if you define binary uploads
from __future__ import print_function # py 2.7 compat.
import ipywidgets as widgets # Widget definitions.
from traitlets import List, Unicode  # Traitlets needed to add synced attributes to the widget.

class FileWidget(widgets.DOMWidget):
    _view_name = Unicode('FilePickerView').tag(sync=True)
    _view_module = Unicode('filepicker').tag(sync=True)
    filenames = List([], sync=True)
    # values = List(trait=Unicode, sync=True)

    def __init__(self, **kwargs):
        """Constructor"""
        super().__init__(**kwargs)

        # Allow the user to register error callbacks with the following signatures:
        #    callback()
        #    callback(sender)
        self.errors = widgets.CallbackDispatcher(accepted_nargs=[0, 1])

        # Listen for custom msgs
        self.on_msg(self._handle_custom_msg)

    def _handle_custom_msg(self, content):
        """Handle a msg from the front-end.

        Parameters
        ----------
        content: dict
            Content of the msg."""
        if 'event' in content and content['event'] == 'error':
            self.errors()
            self.errors(self)

%%javascript
requirejs.undef('filepicker');

define('filepicker', ["jupyter-js-widgets"], function(widgets) {

    var FilePickerView = widgets.DOMWidgetView.extend({
        render: function(){
            // Render the view using HTML5 multiple file input support.
            this.setElement($('<input class="fileinput" multiple="multiple" name="datafile"  />')
                .attr('type', 'file'));
        },

        events: {
            // List of events and their handlers.
            'change': 'handle_file_change',
        },

        handle_file_change: function(evt) { 
            // Handle when the user has changed the file.

            // Save context (or namespace or whatever this is)
            var that = this;

            // Retrieve the FileList object
            var files = evt.originalEvent.target.files;
            var filenames = [];
            var file_readers = [];
            console.log("Reading files:");

            for (var i = 0; i < files.length; i++) {
                var file = files[i];
                console.log("Filename: " + file.name);
                console.log("Type: " + file.type);
                console.log("Size: " + file.size + " bytes");
                filenames.push(file.name);

                // Read the file's textual content and set value_i to those contents.
                file_readers.push(new FileReader());
                file_readers[i].onload = (function(file, i) {
                    return function(e) {
                        that.model.set('value_' + i, e.target.result);
                        that.touch();
                        console.log("file_" + i + " loaded: " + file.name);
                    };
                })(file, i);

                file_readers[i].readAsText(file);
            }

            // Set the filenames of the files.
            this.model.set('filenames', filenames);
            this.touch();
        },
    });

    // Register the FilePickerView with the widget manager.
    return {
        FilePickerView: FilePickerView
    };
});

file_widget = FileWidget()

def file_loaded(change):
    '''Register an event to save contents when a file has been uploaded.'''
    print(change['new'])
    i = int(change['name'].split('_')[1])
    fname = file_widget.filenames[i]
    print('file_loaded: {}'.format(fname))

def file_loading(change):
    '''Update self.model when user requests a list of files to be uploaded'''
    print(change['new'])
    num = len(change['new'])
    traits = [('value_{}'.format(i), Unicode(sync=True)) for i in range(num)]
    file_widget.add_traits(**dict(traits))
    for i in range(num):
        file_widget.observe(file_loaded, 'value_{}'.format(i))
file_widget.observe(file_loading, names='filenames')

def file_failed():
    print("Could not load some file contents.")
file_widget.errors.register_callback(file_failed)


file_widget

A button with the text Browse... should appear stating how many files are selected. Since print statements are included in the file_loading and file_loaded functions you should see filenames and file contents in the output. Filenames and file types are shown in the console log, as well.