What prevents a figure showing before notebook cell completion?

Nessuno ha ancora preso questa issue.

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.

L’issue non indica file sorgente né test. Inizia riproducendo gli esempi con una singola cella e con celle divise usando il backend `%matplotlib widget`, quindi confronta il comportamento di `fig.canvas.draw()` con il backend Qt; il lavoro è completo quando sono state stabilite la causa e un comportamento di rendering appropriato.

Scritto dal modello di indicizzazione a partire dal testo della issue.