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Updates example and docstring to encourage the use of functools.partial in FuncAnimation #20358

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Updates example and docstring to encourage the use of functools.partial in FuncAnimation #20358

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96d4358
Updated example and doctring
jeffreypaul15 Jun 3, 2021
e1b3df7
update example
jeffreypaul15 Jun 3, 2021
b739a44
updated rst and example
jeffreypaul15 Jun 6, 2021
7561a72
Update lib/matplotlib/animation.py
jeffreypaul15 Jun 6, 2021
dff7c58
Update doc/api/animation_api.rst
jeffreypaul15 Jun 8, 2021
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32 changes: 31 additions & 1 deletion doc/api/animation_api.rst
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Expand Up @@ -103,6 +103,7 @@ artist at a global scope and let Python sort things out. For example ::
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
from functools import partial
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@jklymak jklymak Jun 10, 2021 •
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Suggested change
from functools import partial

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@jeffreypaul15 jeffreypaul15 Jun 10, 2021

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Aren't we using partial here?

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@jklymak jklymak Jun 10, 2021

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Not that I can see...

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@jeffreypaul15 jeffreypaul15 Jun 10, 2021

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Sorry, I got confused with the example below


fig, ax = plt.subplots()
xdata, ydata = [], []
Expand All @@ -124,7 +125,36 @@ artist at a global scope and let Python sort things out. For example ::
plt.show()

The second method is to use `functools.partial` to 'bind' artists to
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@story645 story645 Jun 3, 2021

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I think bind is doing too much work here. What about partial is used here to pass arguments to the update method - which separately is kind of confusing since this update method only takes one argument,

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@jeffreypaul15 jeffreypaul15 Jun 3, 2021 •
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So, would increasing the number of arguments be better?

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@story645 story645 Jun 3, 2021

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I think it could make it clearer what partial is doing here

function. A third method is to use closures to build up the required
function. ::

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
from functools import partial

fig, ax = plt.subplots()
xdata, ydata = [], []
ln, = plt.plot([], [], 'ro')

def init():
ax.set_xlim(0, 2*np.pi)
ax.set_ylim(-1, 1)
return ln,

def update(frame):
xdata.append(frame)
ydata.append(np.sin(frame))
ln.set_data(xdata, ydata)
return ln,

ani = FuncAnimation(
fig, partial(update, offset=-0.5),
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@jklymak jklymak Jun 3, 2021

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I guess I'm a good guinea pig for this, as I don't really know what partial is supposed to do. After this I am still mystified 😉. Why wouldn't I just pass update directly here? I don't see where offset ever gets used, so I don't see what the -0.5 means.

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@jeffreypaul15 jeffreypaul15 Jun 3, 2021

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Ah, my bad. I forgot to update update(), I'll make this clearer.

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@story645 story645 Jun 3, 2021

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This should address my issue too

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@tacaswell tacaswell Jun 3, 2021

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This example is also using closures (as update is closing over xdata and ydata). Maybe keep this example dropping the partial to show the closure and switch this example to something like:

def update(frame, x, y):
    x.append(...)
    y.append(....)
    ...

xdata = []
ydata = []
ani = FuncAnimation(fig, partial(update, x=xdata, y=ydata), ...)

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@jeffreypaul15 jeffreypaul15 Jun 6, 2021

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This makes more sense, thanks for the input

frames=np.linspace(0, 2 * np.pi, 128),
init_func=init, blit=True)

plt.show()

A third method is to use closures to build up the required
artists and functions. A fourth method is to create a class.

Examples
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3 changes: 2 additions & 1 deletion lib/matplotlib/animation.py
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Expand Up @@ -1622,7 +1622,8 @@ def init_func() -> iterable_of_artists
value is unused if ``blit == False`` and may be omitted in that case.

fargs : tuple or None, optional
Additional arguments to pass to each call to *func*.
Additional arguments to pass to each call to *func*. Note: the use of
`functools.partial` is preferred over fargs.
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save_count : int, default: 100
Fallback for the number of values from *frames* to cache. This is
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