import io
import panel as pn
pn.extension()

file_input = pn.widgets.FileInput()

file_input

file_input.value

# File
if file_input.value is not None:
    file_input.save('test.png')

# BytesIO object
if file_input.value is not None:
    out = io.BytesIO()
    file_input.save(out)

file_input = pn.widgets.FileInput(accept='.csv,.json')

file_input

file_input = pn.widgets.FileInput(accept='.png', multiple=True)

file_input

pn.Row(file_input.controls(jslink=True), file_input)