matplotlib-users Mailing List for matplotlib

Animation problem of Virgil Stokes.

Since I began the answer sequence, here's a little more. If this 
overlaps other answers, I apologize.

About the third parameter
>> "/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.
I am not trying to accuse you of anything, I simply underline that if 
the documentation - as cited - mentions the word *generator*, and the 
program contains the argument *data_gen*, which is OBVIOUSLY a generator 
which *yields* some data, then this might have give you some clues 
concerning its meaning.

>> 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.

1. Generators might be or not function arguments, keyword or not; this 
is not an issue here. Generators are entities which produce iterators.  
Here you have: *def data_gen(): while True: yield np.random.rand(10)* , 
and this is all.

2. When you see "frames=None", etc., this doesn't absolutely mean that 
it is a kw parameter, just a positional parameter with a default value.
Brendan Barnwell commented this already.
If you look at the definition of the FuncAnimation class, which is 
readable, in the file ... matplotlib/animation.py, you will see
*def __init__(self, fig, func, frames=None, init_func=None, fargs=None, 
save_count=None, **kwargs):**
**   ...*
which explicitly confirms this.

I think that you got the answers you demanded. The FuncAnimation 
callback *requires* one argument, even if you don't use it. It may be 
the frame number (or index if you wish), or explicit, specific data, 
such as in your first example.
If, as in your second example, the parameter passed is the frame index, 
and you want to see how you can use it, test this:

*x=np.linspace(0,20,300)***

*   def update(i):*

**

**

*    data=(np.sin(x+i/3)+1)/2*

**

*    line.set_ydata(data)*

**

***
***

*ani = animation.FuncAnimation(fig, update, interval=40)*


You should see a moving sinusoid.

>>
>> 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".

I don't understand your reaction.  I teach computer science for many 
years, and several times per week I suggest to my students to do this, 
to trace their programs. I trace mine. Nobody feels offended. You said: 
data is undefined. But it WAS DEFINED, you agree? So, printing its value 
was the most natural suggestion. You would immediately see that it had 
been generated by data_gen.

Also, I recommend that you look upon the sources of Matplotlib from time 
to time. I do it regularly, it is nicely commented, and complements very 
well the documentation.

Jerzy Karczmarczuk

PS. Some blizzard around positional/keyword parameters in Python is 
quite persistent.  "Dive into Python" of Mark Pilgrim covers this, and 
offers some useful references.

See also this : https://www.python.org/dev/peps/pep-3102/

"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. :-)"

I am just that good!  No, really though, the book focuses only on a subset
of features in Matplotlib, and it does assume that you are somewhat
comfortable with the language (or at least, understand the basics of Object
Oriented Programming and terminology). There will be another book that will
come out in a few months that is intended to be a complete refresh of
Sandro Toshi's 2009 book that might be more up your alley, but I don't know
how much it will cover of Animations. Sandro's book was released before the
animation module was even a twinkle in Ryan May's eye...

Cheers!
Ben Root


On Thu, Apr 23, 2015 at 1:40 PM, Virgil Stokes <vs...@it...> wrote:

>  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...> 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...> 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>
>>> 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...
>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>>
>>>
>>
>>
>
>

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
>

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
>>
>>
>
>

Brendan, good catch, I didn't notice Virgil's confusion earlier. I think
that is a good explanation. I remember getting very confused by all of that
stuff back when I started in Python. I think mostly because I don't know of
any other language that does argument handling like how Python does it. I
learned it all by "school-of-hard-knocks". Does anybody recommend a really
good online reference that explains the ins-and-outs of positional and
keyword arguments for newbies?

Cheers!
Ben Root


On Thu, Apr 23, 2015 at 1:00 PM, Brendan Barnwell <bre...@br...>
wrote:

> On 2015-04-23 03:22, Virgil Stokes wrote:
> >
> > 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.
>
>         One thing I think may be misleading you is that you seem to be
> misunderstanding how positional and keyword arguments work in Python.
> Specifying a default value for an argument in a function definition
> doesn't mean that you can *only* pass it by keyword when you call it.
> Any named argument can always be passed positionally or by keyword (in
> Python 2).  For instance, if I define a function like this:
>
> def foo(a, b=2):
>      print a+b
>
> I can still call it like this:
>
> foo(8, 10)
>
> I can even call it like this (passing both arguments as keywords "out of
> order")
>
> foo(b=10, a=8)
>
>         Writing "b=2" in the function definition doesn't so much "make b a
> keyword argument" as just "specify a default value for b".  So in the
> FuncAnimation documentation you mentioned, "frames" is not required to
> be a keyword argument, and can still be passed positionally.  (In Python
> 3 there are keyword-only arguments, and even in Python 2 the variadic
> **kwargs syntax collects only keyword arguments, but those aren't
> involved as far as the "frame" argument here is concerned.)
>
> --
> Brendan Barnwell
> "Do not follow where the path may lead.  Go, instead, where there is no
> path, and leave a trail."
>     --author unknown
>
>
> ------------------------------------------------------------------------------
> 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...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>

On 2015-04-23 03:22, Virgil Stokes wrote:
>
> 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.

	One thing I think may be misleading you is that you seem to be 
misunderstanding how positional and keyword arguments work in Python. 
Specifying a default value for an argument in a function definition 
doesn't mean that you can *only* pass it by keyword when you call it. 
Any named argument can always be passed positionally or by keyword (in 
Python 2).  For instance, if I define a function like this:

def foo(a, b=2):
     print a+b

I can still call it like this:

foo(8, 10)

I can even call it like this (passing both arguments as keywords "out of 
order")

foo(b=10, a=8)

	Writing "b=2" in the function definition doesn't so much "make b a 
keyword argument" as just "specify a default value for b".  So in the 
FuncAnimation documentation you mentioned, "frames" is not required to 
be a keyword argument, and can still be passed positionally.  (In Python 
3 there are keyword-only arguments, and even in Python 2 the variadic 
**kwargs syntax collects only keyword arguments, but those aren't 
involved as far as the "frame" argument here is concerned.)

-- 
Brendan Barnwell
"Do not follow where the path may lead.  Go, instead, where there is no 
path, and leave a trail."
    --author unknown

... 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.

Cheers!
Ben Root


On Thu, Apr 23, 2015 at 12:32 PM, Virgil Stokes <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>
>
>
> On Thu, Apr 23, 2015 at 12:05 PM, Virgil Stokes <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>
>> 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...
>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>
>>
>
>

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 <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...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>

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.

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?

Ben Root

<shameless_plug>
P.S. - My new book "Interactive Applications using Matplotlib" has an
entire chapter devoted to animations
</shameless_plug>


On Thu, Apr 23, 2015 at 12:05 PM, Virgil Stokes <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...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>
>

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".

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
>
> 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."
The name "data_gen" could suggest its meaning (after having read the 
doc). Note please that the keyword parameters are specified extra.

> 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.

Please, in such cases test your programs by adding some simple tracing 
contraptions, say, print(data) inside update.

Jerzy Karczmarczuk

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

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.

2. data, the argument to the update function seems to be undefined.

I would appreciate an explanation (in some detail) of how this code actually works.