Can everyone please bring the level of snark/hostility down? Programming
is frustrating, but antagonizing the mailing list does not help anyone.
It is not well documented, but the signature for `func` is assumed to be
`def function(required, *optional_positional)` see
https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/animation.py#L1107
for the line where it actually gets called. The logic behind this is that
the function needs to have some input to know what to draw (so the state
about where in the sequence you are lives in the animation code, not in the
supplied user code).
For passing in the frame data you have several options. The first is to
pass in an iterable of the data you want to be passed to the function (ex
np.arange(5), image_stack, image_generator), basically anything where `it =
iter(input); data = next(it)` 'does the right thing'. The second is to
pass in a callable where repeated calls to `data = my_callable()` 'does the
right thing' This would be useful if you want to reach out and hit some
external hardware for you data each time the animation updates. The last
is to pass in a number of frames, which gets converted into
xrange(frames). In all cases, the Animation turns what ever your input is
into an iterable which gets hit once pre frame (see
https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/animation.py#L1047
for the code version of this paragraph).
Tom
PS was finishing this up as Ben's email came in
On Thu, Apr 23, 2015 at 12:06 PM Virgil Stokes <v...@it.uu.se> wrote:
> Thanks for your reply to my post, Jerzy.
>
>
> On 23-Apr-2015 13:18, Jerzy Karczmarczuk wrote:
>
>
>
> Le 23/04/2015 12:22, Virgil Stokes a écrit :
>
> The following interesting example (random_data.py) is posted at:
>
> http://matplotlib.org/1.4.2/examples/animation/random_data.html
>
>
> import matplotlib.pyplot as plt
> import matplotlib.animation as animation
>
> import numpy as np
>
> Yes, I forgot to include this
>
>
> fig, ax = plt.subplots()
> line, = ax.plot(np.random.rand(10))
> ax.set_ylim(0, 1)
>
> def update(data):
> line.set_ydata(data)
> return line,
>
> def data_gen():
> while True: yield np.random.rand(10)
>
> ani = animation.FuncAnimation(fig, update, data_gen, interval=100)
> plt.show()
>
> This codes works; but, I am very confused by it. For example:
>
> 1. There are 3 positional arguments given for animation.FuncAnimation;
> but, in the
> API documentation for this class (
> http://matplotlib.org/api/animation_api.html), only
> two positional arguments are shown.
>
> The third one is the third one,
> "*frames* can be a generator, an iterable, or a number of frames."
>
> This makes very little sense to me --- what does "or a number of frames"
> mean?
>
> The name "data_gen" could suggest its meaning (after having read the
> doc).
>
> I am not sure what you are referencing as "the doc"; but I did read the
> documentation several times and English is my native language.
>
> Note please that the keyword parameters are specified extra.
>
> I am aware of this. Perhaps, I am a Python dummy --- when I see something
> like value = None in a Python API argument, I interpret this as a keyword
> argument and not a generator.
>
>
> 2. data, the argument to the update function seems to be undefined.
>
> FuncAnimation usually passes the frame number: 0, 1, 2, ... as the first
> parameter of the update function, when "frames" is None, or the number of
> frames. If - as here - the third parameter is a generator, it passes the
> yielded data to update.
> It may be used or not.
>
> Ok, I understand that better now. But, you say "or *the number* of
> frames" but the documentation reads "or *a number* of frames" --- what
> does this mean?
>
> And I still do not understand how to use the first argument of the
> function to be called for the animation. In another animation example (
> histogram.py), the animation function is defined by:
>
> def animate(i):
> # simulate new data coming in
> data = np.random.randn(1000
> n, bins = np.histogram(data, 100)
> top = bottom + n
> verts[1::5,1] = top
> verts[2::5,1] = top
>
> This works of course; but, why is the "i" required? There is no other
> reference to it in the entire script. If I remove it; i.e. use def
> animate(): I get the following error:
>
> TypeError: animate() takes no arguments (1 given)
>
> I do not understand how this explains the fact that the function no longer
> has any arguments. Please explain the meaning of this error message?
>
>
> Please, in such cases test your programs by adding some simple tracing
> contraptions, say, print(data) inside update.
>
> I did this and more before posting my email. I would not have posted this
> unless I thought it was necessary. And I thought one purpose of this user
> group was to help people --- even if they ask a question which may be
> annoying or "stupid" in some subscribers opinion. I try to remember what a
> very wise teacher once said --- "there is no such thing as a stupid
> question".
>
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