Make figures loaded from experiment db viewable in notebook

[ItamarGoldman]

Summary

Make figures loaded from experiment db viewable in jupyter notebook as suggested in #436 .

Details and comments

Some details that should be in this section include:

• Why this change was necessary
  To make it more comfortable to use figures in jupyter notebook.
• What do users and developers need to know about this change
  To display figures of experiment data that were loaded from experiment db don't need to convert to SVG.

[wshanks]

Figures were already made viewable in the notebook by #814 which made .figure() return a FigureData object with special repr methods for Jupyter. I am not sure there is a benefit to modifying the figure attribute like this.

[ItamarGoldman]

Figures were already made viewable in the notebook by #814 which made .figure() return a FigureData object with special repr methods for Jupyter. I am not sure there is a benefit to modifying the figure attribute like this.

I thought that we would like the same behavior for loaded experiment and executed one on Jupyter Notebook.

From what I can see the .figure() method is working as you says, but its output isn't ideal (but maybe its only in my environment) :

while with SVG converter it looks better:

[wshanks]

Oh, you're right. I was testing the initial figure, not the one loaded from the db. For me, loading from the db actually gives no image. For the problem is that in _repr_svg_ here: https://github.com/Qiskit-Extensions/qiskit-experiments/blob/2cc444ac33783ce896662e39cd731b4874f9a0ae/qiskit_experiments/framework/experiment_data.py#L191-L196
self.figure is bytes but then str(self.figure) is just a string starting with b with the Python string representation of the bytes content, not the bytes content decoded as a string. For me, changing str(self.figure) to self.figure.decode("utf-8") resolves the problem. Can you check if that works for you as well? It would be better to fix the repr method than to make the return type variable based on the environment.

[ItamarGoldman]

Oh, you're right. I was testing the initial figure, not the one loaded from the db. For me, loading from the db actually gives no image. For the problem is that in _repr_svg_ here:

https://github.com/Qiskit-Extensions/qiskit-experiments/blob/2cc444ac33783ce896662e39cd731b4874f9a0ae/qiskit_experiments/framework/experiment_data.py#L191-L196

self.figure is bytes but then str(self.figure) is just a string starting with b with the Python string representation of the bytes content, not the bytes content decoded as a string. For me, changing str(self.figure) to self.figure.decode("utf-8") resolves the problem. Can you check if that works for you as well? It would be better to fix the repr method than to make the return type variable based on the environment.

I updated as you suggested and it works 😄 ready for review

[wshanks]

Nice work getting this fixed @ItamarGoldman!

I am approving now, but I left two small suggestions to address before merging.