Support async functions on ParamMethod/ParamFunction

[philippjfr]

Allows an approach like this:

import aiohttp

widget = pn.widgets.IntSlider(start=0, end=10)

async def get_img(index):
    async with aiohttp.ClientSession() as session:
        async with session.get(f"https://picsum.photos/800/300?image={index}") as resp:
            return pn.pane.JPG(await resp.read())
            
pn.Column(widget, pn.bind(get_img, widget))

[codecov]

Codecov Report

Merging #2964 (374436d) into master (1badb73) will decrease coverage by 0.01%.
The diff coverage is 53.84%.

@@            Coverage Diff             @@
##           master    #2964      +/-   ##
==========================================
- Coverage   83.13%   83.11%   -0.02%     
==========================================
  Files         190      190              
  Lines       24875    24885      +10     
==========================================
+ Hits        20680    20684       +4     
- Misses       4195     4201       +6     

Impacted Files	Coverage Δ
panel/param.py	86.92% <53.84%> (-0.82%)	⬇️

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[philippjfr]

Linux 3.6 test failure is spurious.

[MarcSkovMadsen]

Panel will be the most "modern" package in Python :-)

[MarcSkovMadsen]

How would it work with pn.panel(pn.bind(get_img, widget), loading_indicator=True)? Would the loading indicator be shown while the image is being loading async? That would be awesome.

[philippjfr]

Correct! Considering whether to just enable that by default.

[MarcSkovMadsen]

The problem is that if a function is fast, then trying to show the loading indicator actually slows down your application. Or at least it feels like that to the user. And often your function would be fast.

Somehow the loading indicator should first be started after maybe 0.5 seconds or so ??

[philippjfr]

Good point, I think because of that it's probably best left up to the user. Don't want to be in the business of timing user callbacks.