What prevents a figure showing before notebook cell completion?

Nadie ha tomado este issue todavía.

My issue boils down to:

"Why does the figure not show immediately, but instead waits until the cell has completed running?"
```python
%matplotlib widget
import matplotlib.pyplot as plt
from time import sleep
fig = plt.figure()
plt.plot([1,2,3])
sleep(2)
```

This behaviour is preventing fun uses, like dynamic plotting in a single cell:
```python
%matplotlib widget
from matplotlib import pyplot as plt
from time import sleep
import numpy as np
fig = plt.figure()

for i in range(10):
x, y = np.random.random(2)
plt.scatter(x, y)
fig.canvas.draw()
sleep(0.1)
```

The previous code works if one splits it into two cells, placing the `figure()` call in the first one:

```python
# Cell 1
%matplotlib widget
from matplotlib import pyplot as plt
from time import sleep
import numpy as np
fig = plt.figure()

# Cell 2
for i in range(10):
x, y = np.random.random(2)
plt.scatter(x, y)
fig.canvas.draw()
sleep(0.1)
```

Edit: I also note that in the qt backend, there figure and plot are shown immediately, in contrast to the ipympl behaviour.

El issue no menciona archivos fuente ni tests. Empieza reproduciendo los ejemplos de una sola celda y de celdas divididas con el backend `%matplotlib widget` y, después, compara el comportamiento de `fig.canvas.draw()` con el backend de Qt; se considera terminado cuando se hayan establecido la causa y un comportamiento de renderizado adecuado.

Escrito por el modelo de indexación a partir del texto del issue.