observe triggers twice when doing a round trip about ipysheet HOT 3 OPEN

That is really weird... I displayed the traceback using print_stack and it shows that the second external event has not the same origin. We should try to replicate it using a core widget and post an issue in ipywidgets.

In the meantime I can only try to help you with your use case. If what you want to do is format the float numbers in the cells you can do:

import ipysheet

sheet = ipysheet.sheet()
ipysheet.cell(0, 0, -0.4, numeric_format='0.000')
display(sheet)

from ipysheet.

Thanks @martinRenou

numeric_format seems useful. I'd also like to replace non-numeric inputs with the empty string.

I tried to replicate the issue using core widgets (Select.options instead of Cell.value) but didn't succeed.

Let me know if you have any ideas

p.s. Do you think #66 is unrelated?

from ipysheet.

I honestly have no clue. This is really internal behavior of traitlets and ipywidgets and I'm not really aware of it.
But this 'old': ['-0.4000'], 'new': ['-.4'] thingy is really odd, I don't see why it should happen. I guess it's a bug.

The thing is that you are setting the value of the cell in the callback of an observe call, which is not really common use case.
I guess what you would need is a traitlets validator instead?

from ipysheet.