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[Bug]: Incorrect behavior in nbagg when calling plt.figure(num=1) #21957

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ianhi opened this issue Dec 15, 2021 · 3 comments
Open

[Bug]: Incorrect behavior in nbagg when calling plt.figure(num=1) #21957

ianhi opened this issue Dec 15, 2021 · 3 comments
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GUI: nbagg

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@ianhi
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ianhi commented Dec 15, 2021 •
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Bug summary

From matplotlib/ipympl#405 it seems that if you repreatedly run a cell with plt.figure(num=1) and then plot a new line you will only ever have a plot with one line on it.

Code for reproduction

Cell 1

%matplotlib nbagg
import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(-np.pi/2, np.pi/2)
i=0

Cell 2 (run this one repeatedly)

plt.figure(num=1)
plt.plot(x, np.sin(x*i))
i += 1

Actual outcome

nbagg-bug

Expected outcome

Do the equivalent from ipython:

import matplotlib.pyplot as plt
import numpy as np

plt.ion()
x = np.linspace(-np.pi/2, np.pi/2)

# each iteration of loop represents a cell re-execution
i = 0
def run_cell():
    global i
    plt.figure(num=1)
    plt.plot(x, np.sin(x*i))
    i += 1

correct-ipython

Additional information

No response

Operating system

No response

Matplotlib Version

3.5.1

Matplotlib Backend

nbagg

Python version

3.9.7

Jupyter version

6.4.4

Installation

pip
@jklymak
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jklymak commented Dec 15, 2021

That seems like the expected and desired behaviour to me. For a notebook, you definitely don't want the result to depend on how many times you ran a cell.

@QuLogic
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QuLogic commented Dec 15, 2021

plt.figure(num=1) makes the figure with num=1 active. Re-running the cell first clears its outputs, which closes the figure. Thus, there is no figure with num=1 and a new one is created.

So I think I agree with @jklymak that this is expected and intended.

@jklymak
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jklymak commented Dec 15, 2021

Just to be clear, if you want to access an already-open figure, you can stash it as an object and continue to operate on it from other cells.

@tacaswell tacaswell mentioned this issue Dec 15, 2021
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@QuLogic @jklymak @ianhi