output widget append_display_data does not display widgets

[jasongrout]

It seems there are some problems either with the output widget append_display_data method (from #1752), or how we display widgets.

from ipywidgets import Output, IntSlider
out = Output(layout={'border': '1px solid black'})
out.append_display_data(IntSlider())
out

should capture the intslider inside of the output widget, but instead we get

If I use the output widget as a context manager, it works fine:

from ipywidgets import Output, IntSlider
from IPython.display import display
out = Output(layout={'border': '1px solid black'})
with out:
    display(IntSlider())
out

[jasongrout]

From the docs http://ipython.readthedocs.io/en/stable/api/generated/IPython.core.formatters.html:

Prior to IPython 6.1, _ipython_display_ was the only way to display custom mime-types without registering a new Formatter.
IPython 6.1 introduces _repr_mimebundle_ for displaying custom mime-types, so _ipython_display_ should only be used for objects that require unusual display patterns, such as multiple display calls.

We use _ipython_display_, in which we manually call display to display a widget. When we switch to using _repr_mimebundle, I think this issue will resolve itself.

[jasongrout]

IPython 6.1 was released 31 May 2017. I think it will be a while before we can mandate IPython 6.1+ (likely not until ipywidgets 8), so we may just have to live with this for now.

[jasongrout]

actually, we may be able to register a display using the for_type mechanism instead, until we can move to a simple _repr_mimebundle_: http://ipython.readthedocs.io/en/stable/api/generated/IPython.core.formatters.html#IPython.core.formatters.BaseFormatter.for_type

[GaiYu0]

Hi, I am experiencing a similar problem. In my case, the slider widget is displayed properly but the output widget cannot be displayed. Is there any temporary solution?

Thank you very much!

[jasongrout]

@GaiYu0, can you post the code you are using?

[GaiYu0]

It turns out that my problem was caused by broken dependencies, which is irrelevant from this issue. Sorry!

[jasongrout]

actually, we may be able to register a display using the for_type mechanism instead, until we can move to a simple repr_mimebundle: http://ipython.readthedocs.io/en/stable/api/generated/IPython.core.formatters.html#IPython.core.formatters.BaseFormatter.for_type

This won't work. It looks like registering a for_type handler in the ipython display formatter is equivalent to defining the _ipython_display_ function, so it doesn't get us anything more than we had.

So I'm moving this issue into the Major Release milestone, for when we can require ipython >=6.1 and define a _repr_mimebundle_ method.

[jasongrout]

It looks like IPython 6.1 was released May 31, 2017, so we should probably wait until at least June 2018 to make this change.

[jasongrout]

Perhaps we can put in a check for the ipython version, and use the _repr_mimebundle_ if we are in a version that supports it, and otherwise use (monkeypatch?) our class to have the _ipython_display_ method?

[vidartf]

Note: Python allows you to conditionally declare methods, so no monkey-patching would be needed:

In [1]: class A:
   ...:     if True:
   ...:         def sum(self, a, b):
   ...:             return a + b
   ...:

In [2]: a = A()

In [3]: a.sum(5, 6)
Out[3]: 11

In [4]: class B:
   ...:     if False:
   ...:         def sum(self, a, b):
   ...:             return a + b
   ...:

In [5]: b = B()

In [6]: b.sum(5, 6)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-6-b0fbaf787c6b> in <module>
----> 1 b.sum(5, 6)

AttributeError: 'B' object has no attribute 'sum'