Plot is duplicated with repeated calls to plt.show() #585

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1. ianthomas23 commented on Jan 9, 2025

   

   ianthomas23

   on Jan 9, 2025

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   You should not need to call plt.show() when using ipympl. Each Matplotlib Figure that you create (via plt.subplots() or plt.figure() or whatever) is displayed after the code cell in which it is created. Is there a particular reason you are using plt.show()?
2. keatonb commented on Jan 9, 2025

   

   keatonb

   on Jan 9, 2025

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   It may not be needed, but it shouldn't hurt. All matplotlib gallery examples end with plt.show(). I can imagine calling imported functions that call show. Expected behavior is for already displayed to no longer be in the show queue, at least to my understanding, and imported function may expect repeated calls to not duplicate already displayed plots? I haven't downgraded things to check, but I don't think this used to happen with ipympl plots in notebook.
3. ianthomas23 commented on Jan 9, 2025

   

   ianthomas23

   on Jan 9, 2025

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   I cannot reproduce this, see screenshot:

   

   This is using the same package versions:

   Python 3.12.8 | packaged by conda-forge | (main, Dec  5 2024, 14:19:53) [Clang 18.1.8 ] on darwin
   ipympl 0.9.6
   Selected Jupyter core packages...
   IPython          : 8.30.0
   ipykernel        : 6.29.5
   ipywidgets       : 8.1.5
   jupyter_client   : 8.6.0
   jupyter_core     : 5.7.2
   jupyter_server   : 2.14.1
   jupyterlab       : 4.2.5
   nbclient         : 0.8.0
   nbconvert        : 7.16.4
   nbformat         : 5.10.4
   notebook         : 7.2.2
   qtconsole        : 5.6.0
   traitlets        : 5.14.3
   

   and any of matplotlib 3.8.4, 3.9.4 or 3.10.
4. keatonb commented on Jan 9, 2025

   

   keatonb

   on Jan 9, 2025

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   There you made a second figure. Here's a screenshot showing what I mean. Without the ipympl magic, no plot would be displayed after the second call to show.
   
5. ianhi commented on Jan 15, 2025

   

   ianhi

   on Jan 15, 2025

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   The expected behavior is for show() to not repeat the plot output

   I'm not entirely what the expected behavior is. The notebook introduces a new paradigm where the same figure can be displayed multiple times as an output to different cells. In that case it seems intuitive to me that plt.show() should again display the current figure. Although in terminal ipython repeated calls to show does indeed not show the figure multiple times, even if the figure has been closed it will not be shown again.

   I think @timhoffm is the right person to ask about resolving what is the right thing for api consistency, do you have an opinion on the correct behavior?

   ---

   I'm pretty sure that the cause of this behavior is that this display in show is not wrapped in an if statement like this one:

   if manager.canvas.figure in _Backend_ipympl._to_show:

   ipympl/ipympl/backend_nbagg.py

   Lines 458 to 460 in fa3d346

   	try:
   	display(manager.canvas)
   	# metadata=_fetch_figure_metadata(manager.canvas.figure)

   Wrapping that display with the if would likely give the @keatonb their desired behavior.
6. timhoffm commented on Jan 16, 2025

   

   timhoffm

   on Jan 16, 2025

   Last edited by timhoffm

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   I think @timhoffm is the right person to ask about resolving what is the right thing for api consistency, do you have an opinion on the correct behavior?

   My first question is on "The notebook introduces a new paradigm where the same figure can be displayed multiple times as an output to different cells." Is there documentation on this?

   How is that supposed to work? A simple plt.show() should not trigger this. Because one typically doesn't close figures explicitly that would re-show all the figures you've shown anywhere before in the notebook. That's not a reasonable behavior. Or should this only re-show the last figure?

   Either way, what is the use case? If I regard a notebook as a continuous document, having the same figure twice is unneeded duplication. If I want to have an update of the figure, I can re-execute the original cell.

   👍React with 👍1Reacted by Keaton Bell