Notebooks utilizing ipywidgets.Output() don't work with progressive rendering

[timkpaine]

include the following in a cell after the first

class Test(object):
    def __init__(self):
        self.view = ipywidgets.Output()
t = Test()

[martinRenou]

I am not sure I understand this issue... What is not working exactly?

[timkpaine]

The notebook won't render at all, there's more background on gitter

[timkpaine]

#396 might inadvertently fix this

[martinRenou]

Ok, sorry I did not pay attention to the gitter discussion. I will try on my branch and on master.

[martinRenou]

You are talking about this notebook, right?

# Cell 1
import time
from ipywidgets import *
from IPython.display import display

# Cell 2
class Test(object):
    def __init__(self):
        self.layout = Output()
        with self.layout:
            print('Hello world')
        
    def render(self):
        display(self.layout)

# Cell 3
time.sleep(10)
t = Test()

# Cell 4
t.render()

I added the print('Hello world') so that we have something displayed. It seems to work for me both on master and on #396... Might be a race condition

[timkpaine]

What happens if you don't use the output, just instantiate it e.g. remove the with layout

[martinRenou]

Well it does not show anything as expected. The Output is there, just not visible because it's empty.
You could see it if you change its style like self.layout.layout.border = '2px dashed red'. You would see it's there, only it's empty.

[timkpaine]

For me the page spins, and nbconvert hangs on connecting to the existing kernel

[martinRenou]

Weird. I cannot reproduce it locally.

The thing is the current master reconnects to the kernel for each cell... That is fixed in 396, which may be why your use case now works.

[timkpaine]

Yeah I will test to make sure. It was hanging on a wait_for_kernel but since we don't disconnect now it should be fine

[maartenbreddels]

#396 fixes some output issues indeed, I was chasing a different bug for interact, so I think before this PR the outputs were buggy. I'm assuming you problem is also fixed, otherwise feel free to reopen.