Allow users to add new Control classes without implementing a plugin

[hansthen]

@Conengmo

This is a new, smaller implementation of the Control class I implemented earlier. For this PR I focused only on the user's ability to load a new control in user space, without having to write a new plugin. It is not difficult to write a plugin, but it does require knowledge of Jinja. Also, there is quite some boilerplate code involved.

With this Control clas I was able to implement the minimap and ruler plugins, using just a few lines of code.

import folium import streamlit as st from folium import Control, TileLayer from streamlit_folium import st_folium st.set_page_config( page_title="minimap", layout="wide" ) m = folium.Map( location=[39.949610, -75.150282], zoom_start=5, zoom_control=False ) tiles = TileLayer( tiles="OpenStreetMap", show=False, control=False, ) tiles.add_to(m) minimap = Control("MiniMap", tiles) minimap.add_js_link( "minimap_js", "https://cdnjs.cloudflare.com/ajax/libs/leaflet-minimap/3.6.1/Control.MiniMap.min.js" ) minimap.add_css_link( "minimap_css", "https://cdnjs.cloudflare.com/ajax/libs/leaflet-minimap/3.6.1/Control.MiniMap.css" ) minimap.add_to(m) ruler = Control("Ruler", tiles) ruler.add_js_link( "ruler_js", "https://cdn.rawgit.com/gokertanrisever/leaflet-ruler/master/src/leaflet-ruler.js", ) ruler.add_css_link( "ruler_css", "https://cdn.rawgit.com/gokertanrisever/leaflet-ruler/master/src/leaflet-ruler.css", ) ruler.add_to(m) st_folium(m, width=1600, height=600) 

[hansthen]

Closes #1992

[hansthen]

@ocefpaf can you have a look?

[ocefpaf]

One problem that we have in folium templates are the silent erros when passing keywords to it. For example, if someone types bottonright instead of bottomright, it will take user a while to figure out what is wrong.

Maybe we should check for this 4 valid kw? I know this doesn't solve it for all templates, but in this case it may be small enough that it is worth it.

[hansthen]

Do you mean as a static typing check or as an assert?

[ocefpaf]

We should avoid assert use outside of tests.

I'm old school but here is what I would do:

1. make position a kw argument, not an arg;
2. Sanitize it with a position.lower() to validate names copied from leaflet JS docs;
3. Check if the sanitized positions is in a valid list with those 4 names and raise a ValueError if not.

What do you think?

[hansthen]

Makes sense.

[hansthen]

I see we have been inconsistent in banning assert :-)

[ocefpaf]

While I was a Fortran programmer in my early days, type checking is not my forte. (Heck, I moved to Python to get away from this ;-p)

My crude review tells me that this is equivalent to what I described in my review comment, right? If so, merge away!

[hansthen]

I wrote my first program for money in RPG :-) which is a fairly obscure language almost as old as Fortran. Whitespace is significant to a fault.

 C* PARAMETER LIST C *ENTRY PLIST C PARM DATEIN 80 C* PROGRAM START C DATEIN DIV 100 DATEIN C MVR DAY 20 C DATEIN DIV 100 DATEIN C MVR MONTH 20 C Z-ADDDATEIN YEAR 40 C* SHOW RESULTS C YEAR DSPLY C MONTH DSPLY C DAY DSPLY C SETON LR C* EXECUTION EXAMPLE C* CALL SEPDATE PARM(X'019960531F') 

I added one more test.