#!/usr/bin/env python
# coding: utf-8

# In[ ]:


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


# This is a custom widget that allows the user to upload file data to the notebook server.  The file data is sent via a statefull `value` attribute of the widget.  The widget has an upload failed event that fires in the front-end and is echoed to the back-end using a custom msg.

# In[ ]:


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)
    


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get_ipython().run_cell_magic('javascript', '', '\nrequire(["widgets/js/widget", "widgets/js/manager"], function(widget, manager){\n\n    var FilePickerView = widget.DOMWidgetView.extend({\n        render: function(){\n            // Render the view.\n            this.setElement($(\'<input />\')\n                .attr(\'type\', \'file\'));\n        },\n        \n        events: {\n            // List of events and their handlers.\n            \'change\': \'handle_file_change\',\n        },\n       \n        handle_file_change: function(evt) { \n            // Handle when the user has changed the file.\n            \n            // Retrieve the first (and only!) File from the FileList object\n            var file = evt.target.files[0];\n            if (file) {\n\n                // Read the file\'s textual content and set value to those contents.\n                var that = this;\n                var file_reader = new FileReader();\n                file_reader.onload = function(e) {\n                    that.model.set(\'value\', e.target.result);\n                    that.touch();\n                }\n                file_reader.readAsText(file);\n            } else {\n\n                // The file couldn\'t be opened.  Send an error msg to the\n                // back-end.\n                this.send({ \'event\': \'error\' });\n            }\n\n            // Set the filename of the file.\n            this.model.set(\'filename\', file.name);\n            this.touch();\n        },\n    });\n        \n    // Register the DatePickerView with the widget manager.\n    manager.WidgetManager.register_widget_view(\'FilePickerView\', FilePickerView);\n});\n')


# The following shows how the file widget can be used.

# In[ ]:


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