Thank you very much for this pull request, it looks awesome! I should have some feedback for you in a couple of days.

OK, so I think we'd like to merge this in time for the 4.9 release in a few weeks, but one change I would propose would be to include this under plotly.figure_factories rather than plotly.express. In general, ff is where we put code that does a lot of Python-level computation, and doesn't map directly onto an underlying trace type. In this case, there's a fair bit of math happening in Python and we're using the choroplethmapbox trace type, so ff feels like a better fit than px.

What do you think?

PS: overall this is an excellent piece of work, and I can imagine reusing some of these utility functions elsewhere in the codebase, especially for automatic zoomlevel calculations etc, so "bravo"!

At first I hesitated between plotly express and figure factory but it felt to me like figure factory was for more complex plots with multiple elements. Also I made this PR so that the call to hexbin_mapbox respects the plotly.express api, you can even use the animation frames part to see the evolution of the binning. It also reuses the express docstring maker and phrasing.

Now I understand that there is not a traditional mapping between plotly.express and plotly.graph_objs with this one so it'll be your call where you want to put it 😄

And glad that some of the util functions can be reused!

OK, after some thought, I think I would like this to be in the figure_factory module, yes. We're also going to want to have some tests that lock down the behaviour of this function, similar to the ones that test px. Basically you can create a fig with some sample data and make some assertions about the resulting structure.

I'm a little worried about the use of the private build_dataframe function here, as this one saw a lot of churn recently. Hopefully it's under control now but you never know. So I'd definitely like some tests around the hexbin function that would break if I break something inside build_dataframe later :)

Finally, we'll also need a new documentation page with some examples of how to use it. This can just be a new Markdown file in /doc/python or a notebook if you're not into using Jupytext: I'll convert it for you. Once that's done I can add some links to that page from various other doc pages to drive some traffic to it :)

OK, in that case, is it possible to call functions from express in figure_factory or these two should be completely independent and I should only call functions from the lower-level graph_objects?
More specifically, I am currently using choropleth_mapbox as well as the build_dataframe and make_docstring from express and I'm wondering if they can stay if I move this to figure_factory.

I think it's totally fine for a figure factory to call public functions from PX like px.choropleth_mapbox. I'm a little less comfortable with calling functions like make_docstring and build_dataframe but I think it's OK in this case, as the alternative would be much worse :)

I added some tests. For now, I put them in tests/test_optional/test_figure_factory/test_figure_factory.py, not sure if that's the right place for them to be run automatically.
Also, some orca dendrogram tests fail though I have not touched this part of the code.

I'll get on to the doc page soon.

Thanks! The dendrogram error will be fixed soon: #2618

Documentation page added!
Just one question regarding the thumbnail in the meta, I'm not sure where to put it, is it in this repository somewhere?
I created one in case it needs to be uploaded by the Plotly team.

This looks great, thank you! I'll do a couple of fixups in an additional commit and this will be released with 4.9 this week.

Finishing up in #2638 if you want to keep track :)

The thumbnail needs to go up in our S3 bucket, and I've just uploaded it there, FYI. https://images.plot.ly/plotly-documentation/thumbnail/hexbin_mapbox.jpg

Thanks for keeping me updated and for the final tweaks 👍

The thanks go to you, for one of the most complete and obviously-awesome external pull requests I've ever seen :)