rendering issues when exception is raised before cell execution completes

[odedbd]

Reposting from jupyter/notebook issue. The code cell as appears in the screen shot is:

import ipympl
import matplotlib.pyplot as plt

def plot_something():
    plt.figure()
    plt.plot([0,2],[0,2],'-')
    plt.show()

plot_something()
raise Exception

The behavior I am seeing is different for the first time I run the cell and the next times. It is also different for different level of browser zoom levels (I am using Chrome 56.0.2924.87 on Windows 8.1)-

First time that the cell is run -
The figure appears but is not fully rendered (see image)-

If I then resize the figure using the GUI (bottom right corner), the behavior changes based on browser zoom level-

1. When using 100% zoom level (default), the figure is rendered too small. When in this state the zoom rectangle is drawn offset from the mouse pointer. The zooming is determined by the mouse pointer, it is just the drawing of the rectangle that is off.
2. When using 90% zoom level (ctrl^- once), the figure is rendered to size and the zoom rectangle is working fine.

When I rerun the cell the figure is re-rendered properly without need for resizing and independent of zoom level.

[tacaswell]

@odedbd Do you have a high-dpi screen?

[odedbd]

@tacaswell Nope, not HDPI

[asteppke]

I think I ran into something related to this issue. With the following code in the first cell

%matplotlib widget

from matplotlib import pyplot as plt
import numpy as np

x = np.linspace(-4, 4, 100)

fig, ax = plt.subplots(figsize=(2, 2))
ax.plot(x, x**2)

# plt.gcf().canvas.draw()

and in the second cell

raise Exception

when the notebook is started and we use "Cell->Run all" no figure is drawn with the current ipympl. When the cells are individually run after each other the figure shows up correctly. This is a bit annoying in longer notebooks where several figures are created and a typo in the last cell causes an exception and then no single figure shows up above.

By using the extra plt.gcf().canvas.draw() the figure shows up correctly even with the exception later.