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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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34 changes: 32 additions & 2 deletions 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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Aren't we using partial here?

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Not that I can see...

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Sorry, I got confused with the example below


fig, ax = plt.subplots()
xdata, ydata = [], []
Expand All @@ -123,8 +124,37 @@ artist at a global scope and let Python sort things out. For example ::
init_func=init, blit=True)
plt.show()

The second method is to use `functools.partial` to 'bind' artists to
function. A third method is to use closures to build up the required
The second method is to use `functools.partial` to pass arguments to the
function. ::

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

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

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

def update(frame, x, y):
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This is just wrong isn't it? you are appending to x and y and then setting the data with xdata and ydata. I guess I am never clear if x and y are references or not, but at the very least this is confusing...

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I thought the same, hence the use of offset, should I revert to that instead?

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I don't know. I'd not do it this way, so whoever would do it this way should write the doc ;-)

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@tacaswell Suggested the example, would this be better instead :

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

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

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

def update(frame, x_offset=0, y_offset=0):
   xdata.append(frame+x_offset)
   ydata.append(np.sin(frame)+y_offset)
   ln.set_data(xdata, ydata)
   return ln,

x_offset = 2
y_offset = 0.2
ani = FuncAnimation(
fig, partial(update, x_offset=x_offset, y_offset=y_offset),
frames=np.linspace(0, 2 * np.pi, 128),
init_func=init, blit=True)

plt.show()

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I mean the above looks better to me. But I don't understand, at all, why we wouldn't just use globals here. If an example where this is practically better than just using a global, we should write such an example.

x.append(frame)
y.append(np.sin(frame))
ln.set_data(xdata, ydata)
return ln,

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

save_count : int, default: 100
Fallback for the number of values from *frames* to cache. This is
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