How to update matplotlib

[dmenne]

First Check

• I added a very descriptive title here.
• I have checked the FAQs for a similar question and didn't find it.
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Example Code

import numpy as np
from matplotlib import pyplot as plt
from nicegui import ui

with ui.pyplot(close=False) as plot:
    x = np.linspace(0.0, 5.0)
    y = np.cos(2 * np.pi * x) * np.exp(-x)
    plt.plot(x, y, "-")
    ax = plt.gca()


def add_line():
    ax.axhline(0, color="red", linestyle="--")
    plot.update()


ui.button("Add line at y=0", on_click=add_line)

ui.run()

Description

I expected this to plot the line on click.

NiceGUI Version

3.2.0

Python Version

3.13.9

Browser

Chrome

Operating System

Windows

Additional Context

No response

[dmenne]

Ok, found it: #2892,

but I still do not understand why my solution did not work.

[falkoschindler]

I think the main reason is that it is not implemented this way. In contrast to using a with-expression, update() doesn't translate the figure into HTML, so there is no new content to be sent to the client. The intention is to use ui.pyplot with Matplotlibs "pyplot" API (see https://matplotlib.org/stable/users/explain/figure/api_interfaces.html).

For the object-oriented API, I'd recommend using ui.matplotlib:

plot = ui.matplotlib()
with plot.figure as fig:
    x = np.linspace(0.0, 5.0)
    y = np.cos(2 * np.pi * x) * np.exp(-x)
    ax = fig.gca()
    ax.plot(x, y, '-')

def add_line():
    ax.axhline(0, color='red', linestyle='--')
    plot.update()

ui.button('Add line at y=0', on_click=add_line)