Expander

The Expander helper lets you hide and show a block of content under a clickable header. It is useful for optional settings, advanced parameters, explanations, or details that should not be visible by default.

mr.Expander() returns an output area, so you can write content into it using a with block.

Live Demo

You can check the Expander widget directly in this interactive example:

🚀 Load interactive demo Hover to start

🛠️ Source code ⛅ Mercury Cloud

Usage

Call mr.Expander() to create an expander section. The function returns an output widget you can write into.

Basic Example

Code

import mercury as mr

details = mr.Expander(label="Details")

with details:
    print("Hidden content")

Expanded by Default

Use expanded=True to open the expander on first render.

Code

import mercury as mr

details = mr.Expander(
    label="Advanced settings",
    expanded=True
)

with details:
    print("Shown immediately")

Common Pattern: Advanced Options

Code

import mercury as mr

# Basic controls
name = mr.TextInput(label="Name")

# Advanced section
advanced = mr.Expander(label="Advanced")

with advanced:
    threshold = mr.NumberInput(label="Threshold", value=0.5, min=0.0, max=1.0, step=0.05)
    refresh = mr.Checkbox(label="Auto-refresh")

Expander Props

label

type: string

Text displayed in the expander header. The default is "Details".

---

expanded

type: bool

If True, the expander starts in the open state. The default is False.

---

key

type: string

Unique identifier used to distinguish expanders with identical arguments.

Note

If the same code cell is run again, Mercury reuses the previous expander instance unless a different key is specified.

The key value is required when expanders are created inside loops.

---

Notes

• mr.Expander() returns an output area. Put content inside using with.
• The expander uses a single unified border and smooth open/close animation.
• Use expanders for optional or advanced settings to keep the UI clean.