matplotlib-users

Re: [Matplotlib-users] show()

[Jean-Michel P. <jea...@ir...>]

jdh...@ac... wrote:
> In truth, the latest release of matplotlib sets a flag on show to
> prevent repeated calls from doing any real damage.
> 
> But for classroom use, I suggest you just put "interactive : True" in
> your rc file and then you have no need for show.  Is there a downside
> to this approach?
> 
> JDH

It seems that show() hangs if no figure has been created before calling 
(under matplotlib 0.62.4). Am I wrong or is it an unexpected use of show() ?

JM. Philippe

Re: [Matplotlib-users] show()

[Jean-Michel P. <jea...@ir...>]

Ok. Now suppose you write an application that runs a set of algorithms 
not known in advance. These algorithms may or may not create figures 
depending on what they perform; they may also encounter difficulties 
(e.g. not enough input data) so that none of them is finally able to 
create a figure. As this is always better to dissociate code pieces the 
more as possible, I'd prefer not to use a global variable to trace 
figure creation. So is there a way to know that no figure was created?

Regards.

JM.

jdh...@ac... wrote:
>     Jean-Michel> It seems that show() hangs if no figure has been
>     Jean-Michel> created before calling (under matplotlib 0.62.4). Am
>     Jean-Michel> I wrong or is it an unexpected use of show() ?
> 
> show should be the last line of your script.  It is expected to hang.
> It starts the GUI mainloop after which all processing is done in the
> GUI event handling (unless you are using threading).
> 
> See http://matplotlib.sf.net/faq.html#SHOW
> 
> JDH

Re: [Matplotlib-users] show()

[John H. <jdh...@ac...>]

>>>>> "Jean-Michel" == Jean-Michel Philippe <jea...@ir...> writes:

    Jean-Michel> Ok. Now suppose you write an application that runs a
    Jean-Michel> set of algorithms not known in advance. These
    Jean-Michel> algorithms may or may not create figures depending on
    Jean-Michel> what they perform; they may also encounter
    Jean-Michel> difficulties (e.g. not enough input data) so that
    Jean-Michel> none of them is finally able to create a figure. As
    Jean-Michel> this is always better to dissociate code pieces the
    Jean-Michel> more as possible, I'd prefer not to use a global
    Jean-Michel> variable to trace figure creation. So is there a way
    Jean-Michel> to know that no figure was created?

In 0.63, we introduced a flag on the
matplotlib.backends.draw_if_interactive function.  If
draw_if_interactive._called is False, the function was never called
and thus no plotting commands were issued.  You may be able to use
this to decide whether to call show or not.  

Eg , at the end of your script

  if draw_if_interactive._called: show()

Note if you are using a pure image backend (eg agg, svg, ps) you do
not need show at all; this is for GUI backends only.  Just call
savefig anywhere in your code.

But if you really want full control with no magic globals, I suggest
using the matplotlib API rather than the matlab interface.  Here is a
minimal example with the SVG backend to create a figure w/o the matlab
interface

  
  from matplotlib.backends.backend_svg import FigureCanvasSVG
  from matplotlib.figure import Figure
  fig = Figure()
  ax = fig.add_subplot(111)
  ax.plot([1,2,3])
  canvas = FigureCanvasSVG(fig)
  canvas.print_figure('myfile.svg')

There are several examples called embedding_in_*.py at
http://matplotlib.sf.net/examples that show how to do this for your
GUI of choice.

Let me know if you need more help; and be sure to tell which backend
you are targetting.

JDH

Re: [Matplotlib-users] show()

[Jean-Michel P. <jea...@ir...>]

jdh...@ac... wrote:
> In 0.63, we introduced a flag on the
> matplotlib.backends.draw_if_interactive function.  If

I must say I'm really impressed how fast matplotlib gets improved!

> Eg , at the end of your script
> 
>   if draw_if_interactive._called: show()
> 
> Note if you are using a pure image backend (eg agg, svg, ps) you do
> not need show at all; this is for GUI backends only.  Just call
> savefig anywhere in your code.

Perfect! This is exactly what I needed for one of my apps.

> But if you really want full control with no magic globals, I suggest
> using the matplotlib API rather than the matlab interface.  Here is a
> minimal example with the SVG backend to create a figure w/o the matlab
> interface

Well, what do you exactly mean by full control? The fact that the figure 
is no more controlled by matplotlib.matlab (as matlab does) but under my 
own control? So that the application is now fully responsible for 
displaying it? I'm afraid I don't understand why this should remove 
"magic" globals, I feel some globals are still required...

NB: currently I'm targeting TkAgg.


JM. Philippe

Re: [Matplotlib-users] show()

[John H. <jdh...@ac...>]

>>>>> "Jean-Michel" == Jean-Michel Philippe <jea...@ir...> writes:

    Jean-Michel> Perfect! This is exactly what I needed for one of my
    Jean-Michel> apps.

Glad that worked for you.

    >> But if you really want full control with no magic globals, I
    >> suggest using the matplotlib API rather than the matlab
    >> interface.  Here is a minimal example with the SVG backend to
    >> create a figure w/o the matlab interface

    Jean-Michel> Well, what do you exactly mean by full control? The
    Jean-Michel> fact that the figure is no more controlled by
    Jean-Michel> matplotlib.matlab (as matlab does) but under my own
    Jean-Michel> control? So that the application is now fully
    Jean-Michel> responsible for displaying it? 

    Jean-Michel> NB: currently I'm targeting TkAgg.

What I mean is that is that if you want to explicitly control when
your figure windows are shown, you need to use the matplotlib API, and
example of which for tkagg is at
http://matplotlib.sf.net/examples/embedding_in_tk.py.  In this case,
you explicitly make the calls to show or hide your window when you
want.  If you use the matlab interface, you are constrained either to
1) if interactive is False, show all of your figures at the end of the
script when you call show or 2) if interactive is True, show all your
windows at the time of their creation.

Actually, you may have a 3rd (untested, unsupported) option with the
matlab interface.  Thanks to the changes Fernando and I introduced to
support ipython, I believe as of matplotlib 0.62 it is safe to call
show repeatedly without blocking script execution.  You may want to
test this and report back.

    Jean-Michel> I'm afraid I don't understand why this should remove
    Jean-Michel> "magic" globals, I feel some globals are still
    Jean-Michel> required...

Some people do not like to use the matlab interface because it manages
the current figure and axes for them, behind the scenes.  Eg when you
type plot(x,y), the plot command is sent to the current figure and
axes, as in matlab, which are stored as "global" (actually module
level) variables in matplotlib.matlab.  In the matplotlib API, you
have to explicitly instantiate the figure and axes, and direct your
plotting, saving, etc commands to these instances, as in

    from matplotlib.numerix import arange, sin, pi
    from matplotlib.figure import Figure
    f = Figure(figsize=(5,4), dpi=100)
    a = f.add_subplot(111)
    t = arange(0.0,3.0,0.01)
    s = sin(2*pi*t)
    a.plot(t,s)

In a complex, nested application or script, it is sometimes nice to
have this extra degree of clarity.

Hope this helps,
JDH

Re: [Matplotlib-users] show()

[John H. <jdh...@ac...>]

>>>>> "Jean-Michel" == Jean-Michel Philippe <jea...@ir...> writes:


    Jean-Michel> It seems that show() hangs if no figure has been
    Jean-Michel> created before calling (under matplotlib 0.62.4). Am
    Jean-Michel> I wrong or is it an unexpected use of show() ?

show should be the last line of your script.  It is expected to hang.
It starts the GUI mainloop after which all processing is done in the
GUI event handling (unless you are using threading).

See http://matplotlib.sf.net/faq.html#SHOW

JDH