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Re: [Matplotlib-users] animation.FuncAnimation example --- how does it work?
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From: Virgil S. <vs...@it...> - 2015-04-23 17:47:06
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On 23-Apr-2015 18:28, Thomas Caswell wrote: > 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 > This was very useful! > 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 > And also very useful! > 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 <vs...@it... > <mailto:vs...@it...>> 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". > ------------------------------------------------------------------------------ > BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT > Develop your own process in accordance with the BPMN 2 standard > Learn Process modeling best practices with Bonita BPM through live exercises > http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_ > source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_SF_______________________________________________ > Matplotlib-users mailing list > Mat...@li... > <mailto:Mat...@li...> > https://lists.sourceforge.net/lists/listinfo/matplotlib-users > |
