st.download_button widget in Streamlit

The download_button widget is used to display a download button in a Streamlit app. This is useful when you want to provide a way for users to download a file directly from your application.

Basic Syntax

st.download_button(
    label="Download",
    data="This is some text to download.",
    file_name="example.txt",
    mime="text/plain"
)

The function has the following parameters:

label — Text shown on the button.
data — The content to be downloaded (string, bytes, or file-like object).
file_name — Default name of the downloaded file.
mime — MIME type (e.g., "text/plain", "text/csv", "application/pdf").

When the user clicks the button, the browser automatically downloads the file.

Example: Download a CSV file from a DataFrame.

Python

import streamlit as st
import pandas as pd

# Create sample data
data = {
    "Name": ["Alice", "Bob", "Charlie"],
    "Score": [85, 90, 78]
}

# Create DataFrame
df = pd.DataFrame(data)

# Filter rows where Score >= 80
newdf = df[df["Score"] >= 80]

# Display filtered DataFrame
st.write(newdf)

# Convert DataFrame to CSV format
csv_data = newdf.to_csv(index=False)

# Create download button
st.download_button(
    label="📥 Download CSV",
    data=csv_data,
    file_name="student_scores.csv",
    mime="text/csv"
)

Explanation

df.to_csv() converts the DataFrame into a CSV string.
st.download_button() allows users to download the file instantly.

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