feat: Add date_slider input widget

[FBruzzesi]

📝 Summary

This is a proof of concept (maybe headstart?) to introduce a date_slider (edit: actually a date_range_slider) widget.

Fixes #6316

🔍 Description of Changes

• Adds date_slider ui widget
• Arguably too much refactor in the dates.py module
• The frontend is 95% AI generated, that's why I am opening this as a draft, and happy to let anyone take it over. My main objective here was to see how feasible it was to add this component.
• TODO: I would like to add the possibility to use a custom formatting that is applied to the dates before

Screenshot of rendering

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions. Thread link.
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Preview	Comments	Updated (UTC)
marimo-docs	Ready	Preview	Comment	Nov 21, 2025 10:30pm

[FBruzzesi]

The automatic labeling to "documentation" seems off 🫠

[mscolnick]

@akshayka @dmadisetti - curious if you think mo.ui.slider( should support date and datetime in the params, or if we should keep them separate under mo.ui.date_slider

[FBruzzesi]

@mscolnick for context this is a date range slider (I guess I could rename it), meaning start to end.
But in both cases, it would make sense to have those to be generic over a few types. In general I think also custom ordered sequences would be interesting (at least to me)

Screenshot:

[mscolnick]

I think if they are separate sliders, then it would be good rename to include range, but we can wait to see hear feedback if they should be merged.

(I'm leaning towards merging them if it's possible and the api does not get overloaded with different params when a int vs date)

[akshayka]

Neat PR!

I am leaning toward adding two new APIs:

1. date_slider
2. date_range_slider

These are the reasons I prefer adding new APIs:

1. The types are clear. mo.ui.slider(...).value is guaranteed to be numeric, so I can do arithmetic on it without having to check its type
2. I can imagine feature creep related to dates (formatting, timezones) that might not relate to numeric sliders.

That said ... maybe the type concern could be addressed with generics and @overload, which would allow us to keep a single API (example). But that may be too complicated, and it would also be a breaking change because mo.ui.slider would become a function instead of a class.

(If we did use a single API, then I'd suggest we make the change across slider and range_slider at the same time, and also update steps to support date.)

[akshayka]

In general I think also custom ordered sequences would be interesting (at least to me)

@FBruzzesi Can you describe your use case for custom ordered sequences? I am wondering if we just design for that solution instead of special casing dates

[FBruzzesi]

@FBruzzesi Can you describe your use case for custom ordered sequences? I am wondering if we just design for that solution instead of special casing dates

Hey @akshayka 👋🏼

First of all thanks for the patience in this PR, I am really tight these days. And thanks for considering a broader request.

Here a use case I have goes as follows.

I would like to create a range slider with a sequence that has a natural order. Specifically I would want to have a sequence of isoweeks. I build a library iso-week-date to simplify a bunch of operations in python (such as addition, subtraction and comparison), but in general notice that the iso weeks have a natural lexicographical order, e.g. "2025-W01" < "2025-W02").
With the library I can do: IsoWeek.range(start, end, step) and get a range of strings (or IsoWeek objects depending on another parameter).

If I were able to put these values into a slider, I can use such to filter a dataframe by some column (e.g. frame.filter(pl.col("week").is_between(pl.lit(slider.value[0]), pl.lit(slider.value[1]))) to either plot or report metrics in different time periods - this is my actual use case.