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st.expander

Insert a multi-element container that can be expanded/collapsed.

Inserts a container into your app that can be used to hold multiple elements and can be expanded or collapsed by the user. When collapsed, all that is visible is the provided label.

To add elements to the returned container, you can use the with notation (preferred) or just call methods directly on the returned object. See examples below.

By default, all content within the expander is computed and sent to the frontend, even if the expander is closed. To enable lazy execution where content only runs when the expander is open, use on_change="rerun" or pass a callable to on_change. The .open property indicates whether the expander is currently open, letting you conditionally render expensive content.

Note

To follow best design practices and maintain a good appearance on all screen sizes, don't nest expanders.

Function signature[source]

st.expander(label, expanded=False, *, key=None, icon=None, width="stretch", on_change="ignore", args=None, kwargs=None)

Parameters

label (str)

A string to use as the header for the expander. The label can optionally contain GitHub-flavored Markdown of the following types: Bold, Italics, Strikethroughs, Inline Code, Links, and Images. Images display like icons, with a max height equal to the font height.

Unsupported Markdown elements are unwrapped so only their children (text contents) render. Common block-level Markdown (headings, lists, blockquotes) is automatically escaped and displays as literal text in labels.

See the body parameter of st.markdown for additional, supported Markdown directives.

expanded (bool)

If True, initializes the expander in "expanded" state. Defaults to False (collapsed).

key (str, int, or None)

An optional string or integer to use as the unique key for the widget. If this is None (default), a key will be generated for the widget based on the values of the other parameters. No two widgets may have the same key.

When on_change is set to "rerun" or a callable, setting a key lets you read or update the expanded state via st.session_state[key]. For more details, see Widget behavior.

icon (str, None)

An optional emoji or icon to display next to the expander label. If icon is None (default), no icon is displayed. If icon is a string, the following options are valid:

  • A single-character emoji. For example, you can set icon="🚨" or icon="🔥". Emoji short codes are not supported.

  • An icon from the Material Symbols library (rounded style) in the format ":material/icon_name:" where "icon_name" is the name of the icon in snake case.

    For example, icon=":material/thumb_up:" will display the Thumb Up icon. Find additional icons in the Material Symbols font library.

  • "spinner": Displays a spinner as an icon.

width ("stretch" or int)

The width of the expander container. This can be one of the following:

  • "stretch" (default): The width of the container matches the width of the parent container.
  • An integer specifying the width in pixels: The container has a fixed width. If the specified width is greater than the width of the parent container, the width of the container matches the width of the parent container.

on_change ("ignore", "rerun", or callable)

How the expander should respond when the user expands or collapses it. This controls whether the expander tracks state and triggers reruns. on_change can be one of the following:

  • "ignore" (default): The expander doesn't track state. All expander content runs regardless of whether the expander is open or closed. The .open attribute of the expander container returns None.
  • "rerun": The expander tracks state. Streamlit reruns the app when the user expands or collapses the expander. The .open attribute of the expander container returns the current state, which is True if the expander is open and False if it's closed. This lets you skip expensive work when the expander is closed.
  • A callable: The expander tracks state. Streamlit executes the callable as a callback function and reruns the app when the user expands or collapses the expander. The .open attribute of the expander container returns its state like when on_change="rerun". If you need to access the current state inside your callback, fetch it through Session State.

When the expander tracks state, it can't be used inside Streamlit cache-decorated functions.

args (list or tuple or None)

An optional list or tuple of args to pass to the on_change callback.

kwargs (dict or None)

An optional dict of kwargs to pass to the on_change callback.

Returns

(ExpanderContainer)

An ExpanderContainer object with an .open property to return the current state of the expander if the expander tracks state.

Examples

Example 1: Use context management You can use the with notation to insert any element into an expander

streamlit_app.py
import streamlit as st

st.bar_chart({"data": [1, 5, 2, 6, 2, 1]})

with st.expander("See explanation"):
    st.write('''
        The chart above shows some numbers I picked for you.
        I rolled actual dice for these, so they're *guaranteed* to
        be random.
    ''')
    st.image("https://static.streamlit.io/examples/dice.jpg")
Built with Streamlit 🎈

Example 2: Call methods directly

You can call methods directly on the returned object:

streamlit_app.py
import streamlit as st

st.bar_chart({"data": [1, 5, 2, 6, 2, 1]})

expander = st.expander("See explanation")
expander.write('''
    The chart above shows some numbers I picked for you.
    I rolled actual dice for these, so they're *guaranteed* to
    be random.
''')
expander.image("https://static.streamlit.io/examples/dice.jpg")
Built with Streamlit 🎈

Example 3: Programmatically control the expander state

You can use a key to programmatically control the expander state or access the state in callbacks. You must set the on_change parameter for the expander to track state.

streamlit_app.py
import streamlit as st

def toggle_expander():
    st.session_state.summary = not st.session_state.summary

def on_expander_change():
    if st.session_state.summary:
        st.toast("You opened the expander.")
    else:
        st.toast("You closed the expander.")

with st.expander("Open expander", on_change=on_expander_change, key="summary"):
    st.write("This is the expander")

st.button("Toggle expander", on_click=toggle_expander)
Built with Streamlit 🎈

ExpanderContainer

A container returned by st.expander.

ExpanderContainer is a Streamlit container with an .open property for lazy execution. Use with notation or call methods directly on the container to add elements to the expander.

Attributes

open (bool or None)

Whether the expander is open. This is True if the expander is open and False if it's collapsed, or None if state tracking isn't enabled.

Examples

Example 1: Lazy loading content

streamlit_app.py
import streamlit as st
import time

summary = st.expander("Summary", on_change="rerun")

if summary.open:
    with summary:
        with st.spinner("Loading summary..."):
            time.sleep(2)
        st.write("This is the summary")
Built with Streamlit 🎈

Example 2: Conditionally render content outside of the expander

streamlit_app.py
import streamlit as st

summary = st.expander("Summary", on_change="rerun")
with summary:
    st.write("This is the summary")

st.write(
    f"The expander is {':green[open]' if summary.open else ':red[closed]'}."
)
Built with Streamlit 🎈
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