ipywidgets saves new entries to `metadata.widgets.state` on execute and notebook displays a widget for each entry on reload

I am using ipywidgets 4.0 with Jupyter 1.0 (IPython 4.0) in Anaconda 64-bits v4.0 (Python 2.7).

When multiple widgets are displayed, if the user starts the cell again, the widgets seem to be completely cleared and replaced by the new instances. However, if the user saves the notebook, then reopens it (eg, by refreshing the page), the old widgets that should have been cleared reappear (except the first one for each cell execution). This is because ipywidgets cleans up the first widget from the log, but not the subsequent ones.

Code to reproduce the issue:

import ipywidgets
from ipywidgets import IntProgress
from IPython.display import display
from time import sleep
p = IntProgress(min=0, max=100, description="First bar is deleted")
p2 = IntProgress(min=0, max=100, description="Second bar always stays")
display(p)
display(p2)
p.bar_style = 'info'
for i in xrange(100):
    p.value = p.value + 1
    p2.value = p2.value + 1
    sleep(0.01)

Here is a demonstration of the issue (note that it doesn’t matter if the cell execution completes or if it is stopped by user, in both cases the widgets will reappear):

[gnestor]

Thank you, Sylvain! 🙏

[SylvainCorlay]

OK, this is fixed in master! We have a much better model for widgets persistence now.