This Python script demonstrates how to run analyses on user-submitted data files using Panel. It runs a Holoviz Panel webpage with a single Plotly line chart which is fed by a FileInput that accepts only CSVs.

panel_fileinput_demo.py

# python 3.7+
# install dependencies:
# pip install panel pandas plotly
# run it: panel serve --show thisfile.py

import io
import param
import panel as pn
import pandas as pd
import plotly.express as px


class FileInputDemo(param.Parameterized):
    data = param.DataFrame()
    file_input = param.Parameter()

    def __init__(self, **params):
        # set the default state of the file_input param
        # must go before super() for some reason
        self.param.file_input.default = pn.widgets.FileInput(accept=".csv")
        super().__init__(**params)

        # initialize data_pane as a DataFrame pane with an empty pandas DataFrame
        self.data_pane = pn.pane.DataFrame(pd.DataFrame())
        # initialize chart_pane as an empty Plotly chart
        self.chart_pane = pn.pane.Plotly()
        # initialize the str_pane with a string
        self.str_pane = pn.pane.Str("No file uploaded")

    # executed when file_input.value changes, i.e. a file is selected
    @param.depends("file_input.value", watch=True)
    def _parse_file_input(self):
        # get the byte value of the file
        value = self.file_input.value
        # get the file's filename
        self.filename = self.file_input.filename
        # decode it using StringIO
        string_io = io.StringIO(value.decode("utf8"))
        # set self.data to the csv contents of the input
        self.data = pd.read_csv(string_io)

    @param.depends("data", watch=True)
    def _update_(self):
        print("self.data")
        print(self.data)
        # update all panes
        # str_pane can indicate that a file was uploaded
        self.str_pane.object = "File selected: {}".format(self.filename)
        # self.str_pane.object = "File selected"
        # don't replace data_pane, but update its object with a new DataFrame pane object
        self.data_pane.object = pn.pane.DataFrame(self.data).object
        # branch off into other methods if you want
        self._secondary_update_method()

    def _secondary_update_method(self):
        # update chart_pane with a new plotly line chart with the new CSV data
        self.chart_pane.object = px.line(self.data)

    def panel(self):
        # create a Column out of the file input the 3 panes
        return pn.Column(
            self.file_input, self.str_pane, self.data_pane, self.chart_pane
        )


panel = FileInputDemo().panel()
panel.servable()

test.csv