Download Button

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from datetime import date
from shiny import ui, render, App

app_ui = ui.page_fluid(
    ui.h4("Download Example Data"),
    ui.download_button("download_data", "Download CSV File"),
    ui.p("Click the button to download a CSV file with sample data."),
)

def server(input, output, session):
    @render.download_button(filename=f"sample-data-{date.today()}.csv")
    def download_data():
        yield "name,age,city\n"
        yield "Alice,25,New York\n"
        yield "Bob,30,San Francisco\n"
        yield "Charlie,35,Chicago\n"

app = App(app_ui, server)
from datetime import date

from shiny.express import render

@render.download_button(  
    filename=lambda: f"data-{date.today()}.csv",  
    label="Download CSV",  
)  
def download_data():
    yield "name,value\n"
    yield "Alice,100\n"
    yield "Bob,200\n"
from datetime import date
from shiny import ui, render, App

app_ui = ui.page_fluid(
    ui.download_button("download_data", "Download CSV"), 
)

def server(input, output, session):
    @render.download_button(filename=lambda: f"data-{date.today()}.csv")
    def download_data():
        yield "name,value\n"
        yield "Alice,100\n"
        yield "Bob,200\n"

app = App(app_ui, server)
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Relevant Functions

  • ui.download_button
    ui.download_button(id, label, *, icon=None, width=None, **kwargs)

  • ui.download_link
    ui.download_link(id, label, *, icon=None, width=None, **kwargs)

  • @render.download_button
    render.download_button(fn=None, *, filename=None, media_type=None, encoding='utf-8', label='Download', width=None)

  • @render.download_link
    render.download_link(fn=None, *, filename=None, media_type=None, encoding='utf-8', label='Download', width=None)

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Details

A download button triggers a file download when clicked. Use ui.download_button() for a button style, or ui.download_link() for a link style.

To add a download button to your app:

  1. Add ui.download_button() or ui.download_link() to the UI with a unique id and descriptive label. (In Express mode, the button is auto-generated from the function name.)

  2. Create a function with the same name as the button’s id and decorate it with @render.download_button() (or @render.download_link() when pairing with ui.download_link()).

  3. The download function can either:

    • Return a string filepath (for existing files on disk)
    • yield content line by line or chunk by chunk (for generated content or temp files)

  4. Specify the download filename using the filename parameter of @render.download_button(). This can be a string or a function that returns a string (useful for dynamic filenames).

Dynamic Filenames: Use a lambda or function for the filename parameter to create dynamic filenames:

@render.download_button(filename=lambda: f"data-{date.today()}.csv")

Content Types: The download handler can yield any content - CSV data, JSON, text files, images, or binary data. For binary files, yield bytes instead of strings.

Streaming: The yield approach allows streaming large files efficiently without loading the entire file into memory.

See Also: Download Link for the link-styled counterpart of this component, and Output UI which can be used to dynamically generate download buttons based on user inputs or reactive values.

Variation Showcase

A live kitchen sink of all possible parameters for the Download Button in Shiny Core and Shiny Express.

Live Core App

Live Express App

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