Merge pull request matplotlib#24238 from oscargus/mpl-20326

Update example and docstring to encourage the use of functools.partial in FuncAnimation

Author: ksunden

doc/api/animation_api.rst

@@ -108,7 +108,7 @@ this means that the callable objects you pass in must know what
 artists they should be working on.  There are several approaches to
 handling this, of varying complexity and encapsulation.  The simplest
 approach, which works quite well in the case of a script, is to define the
-artist at a global scope and let Python sort things out.  For example ::
+artist at a global scope and let Python sort things out.  For example::
 
    import numpy as np
    import matplotlib.pyplot as plt
@@ -133,8 +133,36 @@ 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()
+   line1, = ax.plot([], [], 'ro')
+
+   def init():
+       ax.set_xlim(0, 2*np.pi)
+       ax.set_ylim(-1, 1)
+       return line1,
+
+   def update(frame, ln, x, y):
+       x.append(frame)
+       y.append(np.sin(frame))
+       ln.set_data(x, y)
+       return ln,
+
+   ani = FuncAnimation(
+       fig, partial(update, ln=line1, x=[], y=[]),
+       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

lib/matplotlib/animation.py

@@ -1519,12 +1519,24 @@ class FuncAnimation(TimedAnimation):
     func : callable
         The function to call at each frame.  The first argument will
         be the next value in *frames*.   Any additional positional
-        arguments can be supplied via the *fargs* parameter.
+        arguments can be supplied using `functools.partial` or via the *fargs*
+        parameter.
 
         The required signature is::
 
             def func(frame, *fargs) -> iterable_of_artists
 
+        It is often more convenient to provide the arguments using
+        `functools.partial`. In this way it is also possible to pass keyword
+        arguments. To pass a function with both positional and keyword
+        arguments, set all arguments as keyword arguments, just leaving the
+        *frame* argument unset::
+
+            def func(frame, art, *, y=None):
+                ...
+
+            ani = FuncAnimation(fig, partial(func, art=ln, y='foo'))
+
         If ``blit == True``, *func* must return an iterable of all artists
         that were modified or created. This information is used by the blitting
         algorithm to determine which parts of the figure have to be updated.
@@ -1563,7 +1575,8 @@ 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*. See *func* for details.
 
     save_count : int, default: 100
         Fallback for the number of values from *frames* to cache. This is