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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 17:41:04
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On 23-Apr-2015 18:48, Benjamin Root wrote: > ... keeping conversation on-list ... > > The reason why you get that error is because you took out the argument from > the call signature. But, FuncAnimation assumes that it can send in at least > one argument. That argument is not optional, even if you aren't using it. So, > animate() was called with an argument by FuncAnimation internally, but since > animate() as defined by you did not have that argument, it fails. Ok --- thanks again for the clarification. Who knows, with a little help from this list, I might someday be able to create some useful animations with Matplotlib ;-) > > Cheers! > Ben Root > > > On Thu, Apr 23, 2015 at 12:32 PM, Virgil Stokes <vs...@it... > <mailto:vs...@it...>> wrote: > > On 23-Apr-2015 18:25, Benjamin Root wrote: >> The documentation should say "the number", not "a number". This >> particular argument expects either a generator, an iterable, or an >> integer. If none is given, it will try and figure out something for >> itself. The integer is used to create a number generator, and so you >> effectively have an iterable that supplies the first argument to the >> animation function. > Ok Benjamin :-) --- thanks for the clarification. >> >> Often times, the first argument to this function is just a frame index. >> It is quite possible that you don't need it at all, but it is a part of >> the defined API that the FuncAnimation assumes to be able to call the >> user-supplied function. >> >> Does that help? > Yes, this does indeed help. But I am still puzzled by the error message > given when I remove the argument to the animate function. >> >> Ben Root >> >> <shameless_plug> >> P.S. - My new book "Interactive Applications using Matplotlib" has an >> entire chapter devoted to animations >> </shameless_plug> > Thanks for this also Ben --- I will quite likely get this book. However, considering the complexity of Matplotlib --- only 174 pages bothers me a little. :-) > >> >> >> On Thu, Apr 23, 2015 at 12:05 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 >> >> > > |
