matplotlib-users — Discussion related to using matplotlib

[Matplotlib-users] Re: minor gtk issues with 0.64

[Steve C. <ste...@ya...>]

On Tue, 2004-11-09 at 12:24, matthew arnison wrote:
> 2. I was getting errors that the 
> matplotlib.backends.backend_mod.IMAGE_FORMAT attribute was not
> found, during toolbar initialization. I put in a workaround.

Is this happening when using the classes directly rather than using the
matlab interface? Are you doing something similar to the example
"embedding_in_gtk2.py" - that works OK for me.
Could you provide a minimal example to demonstrate this.

Steve

[Matplotlib-users] Re: could not load matplotlib icon

[Steve C. <ste...@ya...>]

On Wed, 2004-11-10 at 12:16,
mat...@li... wrote:
> John Hunter wrote:
> > Perhaps it would be better to define a constant in
> > matplotlib.__init__.py, something like
> > 
> > matplotlib.PY2EXE = hasattr(sys, 'frozen')
> > 
> > because then the code which is conditional upon py2exe would be more
> > readable
> > 
> >         if not matplotlib.PY2EXE
> >            pygtk.require('2.0')
> > 
> > or something like that...
> 
> Except that Py2EXE is not the only method of "freezing" apps. In 
> particular, you'd want this to work with OS-X's Py2App, and probably 
> other methods of bundling apps.
> 
> you might want:
> 
> matplotlib.FROZEN = hasattr(sys, 'frozen')
> 
> and
> 
> if not matplotlib.FROZEN
>     pygtk.require('2.0')
> 
> Then you could also accommodate other keywords that other bundling 
> methods use.
> 
> BTW, is someone really successfully using PyGTK on Windows? Cool!
> 
> -Chris
I added matplotlib.FROZEN to matplotlib.__init__.py.
It did not work because matplotlib has not yet been imported when 
pygtk.require() is called. So I changed the import order and it seems to
be working on now.

Steve

[Matplotlib-users] pycxx

[Greg N. <no...@uc...>]

I upgraded to Fedora Core 3 and hence spent some time rebuiding all of
the Python modules I use frequently...  

In order to compile matplotlib, I had to install pycxx as a separate
package.  I noticed that there was a cxx directory in the matplotlib
tree, but it didn't seem to be using it.

I got it to compile and it seems to be working.  This message is just
for someone's information to point out the dependency, or the fact
that the stuff in the cxx directory doesn't seem to be satisfying it.

Greg

[Matplotlib-users] Legend for a single line

[Dominique O. <Dom...@po...>]

Hello,

I am experimenting with legends in Matplotlib 0.64 on WinXP.
I notice that when plotting at least two lines, the legend text appears 
horizontally, as expected, e.g. as in:

 >>> plot( [1,2,3], [4,5,6], [1,2,3], [-1,-3,-1] )
 >>> legend( ( 'line1', 'line2' ), 'lower right' )
 >>> show()

However, if I plot only one line, the legend appears vertically:

 >>> plot( [1,2,3], [4,5,6] )
 >>> legend( ( 'line1' ), 'lower right' )
 >>> show()

Finally,

 >>> plot( [1,2,3], [4,5,6] )
 >>> legend( ( 'line1', ), 'lower right' )
 >>> show()

(note the comma after 'line1') produces the horizontal text.

This isn't a big deal, but I am not sure where in legend.py I should fix 
that.

Thanks,
Dominique

Re: [Matplotlib-users] In 0.64 POLAR caannot be imported

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

>>>>> "Al" == Al Schapira <a.d...@wo...> writes:

    Al> Hi John, I just installed 0.64 apparently
    Al> successfully. However, none of the examples run because POLAR
    Al> cannot be imported.  I always get something like this:

    Al> [ads@ADS1 examples]$ python logo.py Traceback (most recent
    Al> call last): File "logo.py", line 3, in ?  from
    Al> matplotlib.matlab import * File
    Al> "/usr/local/lib/python2.3/site-packages/matplotlib/matlab.py",
    Al> line 162, in ?  from axes import Axes, PolarAxes File
    Al> "/usr/local/lib/python2.3/site-packages/matplotlib/axes.py",
    Al> line 9, in ?  from artist import Artist File
    Al> "/usr/local/lib/python2.3/site-packages/matplotlib/artist.py",
    Al> line 4, in ?  from transforms import identity_transform File
    Al> "/usr/local/lib/python2.3/site-packages/matplotlib/transforms.py",
    Al> line 189, in ?  from _transforms import IDENTITY, LOG10,
    Al> POLAR, Func, FuncXY ImportError: cannot import name POLAR

Please see my previous post with subject 

"if you have troubles installing"

[Matplotlib-users] In 0.64 POLAR caannot be imported

[Al S. <a.d...@wo...>]

Hi John,

I just installed 0.64 apparently successfully. However, none
of the examples run because POLAR cannot be imported.
I always get something like this:

[ads@ADS1 examples]$ python logo.py
Traceback (most recent call last):
  File "logo.py", line 3, in ?
    from matplotlib.matlab import *
  File "/usr/local/lib/python2.3/site-packages/matplotlib/matlab.py",
line 162,
in ?
    from axes import Axes, PolarAxes
  File "/usr/local/lib/python2.3/site-packages/matplotlib/axes.py", line
9, in ?    from artist import Artist
  File "/usr/local/lib/python2.3/site-packages/matplotlib/artist.py",
line 4, in ?
    from transforms import identity_transform
  File
"/usr/local/lib/python2.3/site-packages/matplotlib/transforms.py", line
189, in ?
    from _transforms import IDENTITY, LOG10, POLAR, Func, FuncXY
ImportError: cannot import name POLAR

I'm on Redhat linux 9 and have installed every version
of matplotlib since 0.50.

What gives?

Thanks.

	-Al

Re: [Matplotlib-users] Re: could not load matplotlib icon

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

>>>>> "Chris" == Chris Barker <Chr...@no...> writes:

    Chris> BTW, is someone really successfully using PyGTK on Windows?
    Chris> Cool!

I've deployed pretty complex pygtk apps on windows, that incorporate
matplotlib and VTK.  Works great - my windows user have never
complained.

Of course I had to write the vtk gtkglext render window myself....

Really, though, I've been extremely happy with gtk on windows - more
so than on OSX, actually.

JDH

Re: [Matplotlib-users] Re: could not load matplotlib icon

[Chris B. <Chr...@no...>]

John Hunter wrote:
> Perhaps it would be better to define a constant in
> matplotlib.__init__.py, something like
> 
> matplotlib.PY2EXE = hasattr(sys, 'frozen')
> 
> because then the code which is conditional upon py2exe would be more
> readable
> 
>         if not matplotlib.PY2EXE
>            pygtk.require('2.0')
> 
> or something like that...

Except that Py2EXE is not the only method of "freezing" apps. In 
particular, you'd want this to work with OS-X's Py2App, and probably 
other methods of bundling apps.

you might want:

matplotlib.FROZEN = hasattr(sys, 'frozen')

and

if not matplotlib.FROZEN
    pygtk.require('2.0')

Then you could also accommodate other keywords that other bundling 
methods use.

BTW, is someone really successfully using PyGTK on Windows? Cool!

-Chris



-- 
Christopher Barker, Ph.D.
Oceanographer
                                     		
NOAA/OR&R/HAZMAT         (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chr...@no...

Re: [Matplotlib-users] minor gtk issues with 0.64

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

>>>>> "matthew" == matthew arnison <ma...@ca...> writes:


    matthew> 1. I had to change

      toolbar = NavigationToolbar(canvas)
    matthew> to

      toolbar = NavigationToolbar(canvas, win)

    matthew> where win is the GTK window object. I guess the
    matthew> matplotlib API is still unstable. :)

Oops.  This one slipped under my radar screen.  Sorry I didn't
announce it as an API change.  This also break
examples/embedding_in_gtk2.py, for the same reason (fixed in CVS).

Thanks for letting us know...
JDH

Re: [Matplotlib-users] Re: could not load matplotlib icon

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

  Steve> I changed the code in cvs to
        import pygtk
        if not hasattr(sys, 'frozen'):
           pygtk.require('2.0')

  Steve> I think that should fix it.

Perhaps it would be better to define a constant in
matplotlib.__init__.py, something like

matplotlib.PY2EXE = hasattr(sys, 'frozen')

because then the code which is conditional upon py2exe would be more
readable

        if not matplotlib.PY2EXE
           pygtk.require('2.0')

or something like that...

JDH

[Matplotlib-users] Re: could not load matplotlib icon

[Steve C. <ste...@ya...>]

On Tue, 2004-11-09 at 20:14, matthew arnison wrote:
> Thanks heaps. That made things quiet once more.
> 
> While I was in there I noticed the stanza at the top which includes:
> 
> import pygtk
> pygtk.require('2.0')
> 
> Can I suggest wrapping this with a check for py2exe? Like so:
> 
> if not hasattr(sys, 'frozen'):
>      import pygtk
>      pygtk.require('2.0')
> 
> This is because pygtk.require does not work with py2exe.
I changed the code in cvs to
import pygtk
if not hasattr(sys, 'frozen'):
    pygtk.require('2.0')

I think that should fix it.

Steve

[Matplotlib-users] 0.64 windows installation problem ?

[Gary <pa...@in...>]

Did I do something wrong?

After installing from the windows installer, from a DOS window:

Python 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit (Intel)] on 
win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> from matplotlib.matlab import *
Traceback (most recent call last):
 File "<stdin>", line 1, in ?
 File "C:\Python23\Lib\site-packages\matplotlib\matlab.py", line 162, in ?
   from axes import Axes, PolarAxes
 File "C:\Python23\Lib\site-packages\matplotlib\axes.py", line 9, in ?
   from artist import Artist
 File "C:\Python23\Lib\site-packages\matplotlib\artist.py", line 4, in ?
   from transforms import identity_transform
 File "C:\Python23\Lib\site-packages\matplotlib\transforms.py", line 
189, in ?
   from _transforms import IDENTITY, LOG10, POLAR, Func, FuncXY
ImportError: cannot import name POLAR
 >>>

[Matplotlib-users] if you have troubles installing

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

If you have any trouble installing matplotlib, particularly if you get
error messages along the lines of 

  File "C:\Python23\Lib\site-packages\matplotlib\transforms.py", line
189, in ?
    from _transforms import IDENTITY, LOG10, POLAR, Func, FuncXY
ImportError: cannot import name POLAR
 >>>

Try removing site-packages/matplotlib and reinstalling.


JDH

[Matplotlib-users] Re: could not load matplotlib icon

[matthew a. <ma...@ca...>]

Thanks heaps. That made things quiet once more.

While I was in there I noticed the stanza at the top which includes:

import pygtk
pygtk.require('2.0')

Can I suggest wrapping this with a check for py2exe? Like so:

if not hasattr(sys, 'frozen'):
     import pygtk
     pygtk.require('2.0')

This is because pygtk.require does not work with py2exe.

I guess this really a bug in pygtk. But since it is a show stopper at 
deployment time (as I discovered), I suggest it is important enough to 
provide this work around in matplotlib.

Cheers,
Matthew.

Steve Chaplin wrote:
> On Tue, 2004-11-09 at 12:24,
> mat...@li... wrote:
> 
>>Hi,
>>
>>I keep getting this error when my matplotlib gtk app starts up:
>>
>>Could not load matplotlib icon: Couldn't recognize the image file 
>>format 
>>for file 'C:\Python23\share\matplotlib\matplotlib.svg'
>>
>>I don't *think* it's my fault. It doesn't seem to do any harm but it's
>>untidy all the same.
>>
>>Any suggestions?
>>
>>Cheers,
>>Matthew.
> 
> 
> It looks like the problem is happening because your version of GTK does
> include a GDK pixbuf loader for SVG files.
> 
> You can disable the message by editing the installed backend_gtk.py
> (or editing the source file
> matplotlib\lib\matplotlib\backends\backend_gtk.py
> and reinstalling)
> and changing
> "verbose.report_error('Could not load matplotlib icon: %s' %
> sys.exc_info()[1])"
> to 
> "verbose.report('Could not load matplotlib icon: %s' %
> sys.exc_info()[1])"
> or just "pass".
> 
> The fix has also been applied to CVS.
> 
> Steve
> 

[Matplotlib-users] Re: could not load matplotlib icon

[Steve C. <ste...@ya...>]

On Tue, 2004-11-09 at 12:24,
mat...@li... wrote:
> Hi,
> 
> I keep getting this error when my matplotlib gtk app starts up:
> 
> Could not load matplotlib icon: Couldn't recognize the image file 
> format 
> for file 'C:\Python23\share\matplotlib\matplotlib.svg'
> 
> I don't *think* it's my fault. It doesn't seem to do any harm but it's
> untidy all the same.
> 
> Any suggestions?
> 
> Cheers,
> Matthew.

It looks like the problem is happening because your version of GTK does
include a GDK pixbuf loader for SVG files.

You can disable the message by editing the installed backend_gtk.py
(or editing the source file
matplotlib\lib\matplotlib\backends\backend_gtk.py
and reinstalling)
and changing
"verbose.report_error('Could not load matplotlib icon: %s' %
sys.exc_info()[1])"
to 
"verbose.report('Could not load matplotlib icon: %s' %
sys.exc_info()[1])"
or just "pass".

The fix has also been applied to CVS.

Steve

[Matplotlib-users] Subplots.

[<na...@te...>]

Hello,

Matplotlib has been helping me a lot with my graphic needs. I am
still surprised by the looking of the pictures. Many thanks for
the great software.

I'm having some issues, though. Sometimes I get error messages,
usually an error in KERNEL32.DLL on Windows ME, and on Windows
only, I don't get this behaviour in Linux. It's not as bad as it
may seem, as every script runs completely, the pictures are saved
and, besides the message box informing the error, nothing weird
happens. I don't know how to reproduce the errors - when I run
from the DOS prompt or from IDLE, I get the messages. When I
run from my IDE (I use PSPad) I usually don't get error messages,
with the same scripts. Any hint to what I can be doing wrong, or
how to find out what is happening?

Also, I'm in need of some help. I must draw six subplots, one below
the other (subplot(6, ...)), but the way things are coming out, the
plots are to thin, and, although the picture looks good, I thought
that if I could make each subplot a little bigger, that would help
a lot. Is there any way this can be done?

In other plots, I need to index the subplots (label them '(a)',
'(b)', ... for reference in text). I was using xlabel to do that,
but when I have more than two subplots, the xlabel is shadowed by
the following subplot. Is there any way to make the space between
the plots bigger, so the xlabels can be shown, or is there any
other (better) way to do that?

Thanks in advance.

---
José Alexandre Nalon
na...@te...

[Matplotlib-users] could not load matplotlib icon

[matthew a. <ma...@ca...>]

Hi,

I keep getting this error when my matplotlib gtk app starts up:

Could not load matplotlib icon: Couldn't recognize the image file format 
for file 'C:\Python23\share\matplotlib\matplotlib.svg'

I don't *think* it's my fault. It doesn't seem to do any harm but it's 
untidy all the same.

Any suggestions?

Cheers,
Matthew.

[Matplotlib-users] minor gtk issues with 0.64

[matthew a. <ma...@ca...>]

Thanks for matplotlib 0.64. Great to see steady improvements continue to 
roll in.

First the good news. IPython (0.6.4) using pylab works for me again. It 
broke with 0.63 / 0.6.3 and gtk 2.4.x, complaining about gtk mainloop 
and gtk main in the middle of the IPython prompt and then freezing up.

I had some minor issues with my GTK matplotlib API code.

1. I had to change

toolbar = NavigationToolbar(canvas)

to

toolbar = NavigationToolbar(canvas, win)

where win is the GTK window object. I guess the matplotlib API is still 
unstable. :)

2. I was getting errors that the 
matplotlib.backends.backend_mod.IMAGE_FORMAT attribute was not found, 
during toolbar initialization. I put in a workaround.

works with matplotlib 0.63:

import matplotlib
matplotlib.use('GTK')

from matplotlib.backends.backend_gtk import FigureCanvasGTK
from matplotlib.backends.backend_ps import FigureCanvasPS
from matplotlib.backends.backend_gtk import NavigationToolbar2GTK as 
NavigationToolbar

using matplotlib 0.64:

import matplotlib
matplotlib.use('GTK')
from matplotlib.backends import backend_gtk
matplotlib.backends.backend_mod = backend_gtk

from matplotlib.backends.backend_gtk import FigureCanvasGTK
from matplotlib.backends.backend_ps import FigureCanvasPS
from matplotlib.backends.backend_gtk import NavigationToolbar2GTK as 
NavigationToolbar

This style was cribbed from matplotlib examples and / or emails on this 
list.

Cheers,
Matthew.

[Matplotlib-users] ANN: matplotlib-0.64

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

This announcement, with links, is available at
http://matplotlib.sf.net/whats_new.html.

What's new in matplotlib-0.64

  * polar plots - polar plots with the polar command.  These create a
    axes.PolarAxes instance, which defines the default axes,
    gridlines, etc.  Other plot types can be used on polar axes, eg
    scatter.  See examples/polar_demo.py, examples/polar_scatter.py
    and screenshot at
    http://matplotlib.sf.net/screenshots.html#polar_demo.

  * cairo backend - Steve Chaplin has contributed cairo and gtkcairo
    backends - http://cairographics.org.  Cairo is a vector graphics
    library designed to provide high-quality display and print
    output. Currently supported output targets include the X Window
    System, OpenGL, in-memory image buffers, and image files (PNG and
    PostScript).  See http://matplotlib.sf.net/backends.html#Cairo for
    details and install instructions

  * ipython integration - Fernando has continued his excellent work
    integrating matplotlib with ipython and a number of pylab bugs
    have been ironed out.  matplotlib has incorporated ipython's
    numutils in the matplotlib.mlab module - See IPython-0.6.4 - all
    similarities betwen matplotlib and ipython version numbers are
    purely coincidental.

  * Jochen Voss has made a number of bugfixes and improvements to the
    postscript backend, including text layout problems.  PS backend
    should now be DSC compliant.

  * xticks and yticks now take kwargs so you can do, for example

        xticks( arange(3), ('Tom', 'Dick', 'Harry'), fontsize=14 )

  * imshow now supports PIL images - see examples/image_demo3.py.
    Thanks Andrew Straw.

  * barh for horizontal bar charts.  See examples/barh_demo.py

  * added a verbose class to allow different levels of verbosity - see
    http://matplotlib.sf.net/.matplotlibrc for details.  Eg, you can
    now do 

     > python myscript.py --verbose-helpful

    to get a lot of information about what matplotlib is doing behind
    the scenes, what resource files are being used etc.  The default
    verbose settings and file handles for reporting are customizable
    in rc.

  * numerous small bugfixes and improvements: fixes for gcc-3.4, allow
    -dsomeflag where someflag is not a backend, errorbar now accepts
    barsabove to determine the plot order of the errorbar markers and
    lines, fixed a corrcoef bug where args is a matrix, Andrew Dalke
    contributed code to extend the strftime range to the new matplotlib
    date range, fixes to support for python2.2


Downloads at
http://sourceforge.net/project/showfiles.php?group_id=80706&package_id=82474&release_id=281218

Enjoy!
JDH 

Re: [Matplotlib-users] Re: xlabel fontsize

[Paul B. <ba...@st...>]

Chris wrote:

> Dear Xavier,
>
> I am also a brand new user. I can use this one to set the fontsize 
> which may be useful for you.
>
> xlabel('Points', fontsize=30)

Xavier,

Also note that absolute and relative font sizes are allowed, e.g. 
fontsize = 'large' or fontsize = 'larger'.  This usage uses the default 
font size to scale up or down the particular text that you are drawing.  
To scale up all fonts proportionally, just change the default font 
size.  This is easier than using font sizes in points as in the previous 
example.

See the documentation about fonts at 
http://matplotlib.sourceforge.net/fonts.html

 -- Paul

> Xavier MERIAUX wrote:
>
>> Hi,
>>
>> Could you tell me if it is possible to control the fontsize of the x 
>> and ylabel. I can't found anything about this in the tutorial ...
>>
>> I tried without success :
>>
>> plot([1,2,3])
>> x_label = get(gca(), "xlabel")
>> set(x_label,fontsize=30)
>> xlabel('Points')
>> show()
>>
>> Thanks a lot,
>>
>> Xavier.
>

-- 

Paul Barrett, PhD      Space Telescope Science Institute
Phone: 410-338-4475    ESS/Science Software Branch
FAX:   410-338-4767    Baltimore, MD 21218

[Matplotlib-users] Re: xlabel fontsize

[Chris <bi...@Fu...>]

Dear Xavier,

I am also a brand new user. I can use this one to set the fontsize which 
may be useful for you.

xlabel('Points', fontsize=30)

Best regards,
Chris

Xavier MERIAUX wrote:
> Hi,
> 
> Could you tell me if it is possible to control the fontsize of the x and 
> ylabel. I can't found anything about this in the tutorial ...
> 
> I tried without success :
> 
> plot([1,2,3])
> x_label = get(gca(), "xlabel")
> set(x_label,fontsize=30)
> xlabel('Points')
> show()
> 
> Thanks a lot,
> 
> Xavier.
> 
> 
> 
> -------------------------------------------------------
> This SF.Net email is sponsored by:
> Sybase ASE Linux Express Edition - download now for FREE
> LinuxWorld Reader's Choice Award Winner for best database on Linux.
> http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click

[Matplotlib-users] xlabel fontsize

[Xavier M. <Me...@mr...>]

Hi,

Could you tell me if it is possible to control the fontsize of the x and 
ylabel. I can't found anything about this in the tutorial ...

I tried without success :

plot([1,2,3])
x_label = get(gca(), "xlabel")
set(x_label,fontsize=30)
xlabel('Points')
show()

Thanks a lot,

Xavier.

[Matplotlib-users] Re: How to draw an arrow using matplotlib

[Chris <bi...@Fu...>]

Thanks a lot for the very very detail reply. I can not find the time to 
do it by myself at the moment. I will come back to this issue again 
after 2 two weeks.

Best regards,
Chris

John Hunter wrote:
>>>>>>"Chris" == Chris  <Ch...@Fu...> writes:
> 
> 
>     Chris> Dear friends, I just start to use matplotlib, which looks
>     Chris> quite promising for me. I need to draw a couple of arrows
>     Chris> in my 2D plot. Is there a simple way to get it work?
> 
>     Chris> Any suggustions are welcome.
> 
> I recommend creating an arrow class, derived from matplotlib.artist.Artist, that
> contains a matplotlib.lines.Line2D for the arrow stem and a
> matplotlib.patches.RegularPolygon  with numVertices=3 for the arrow
> head.  You can control the rotation of the arrowhead with the
> orientation argument.  
> 
> Once you have this class so defined, you can add it instances of it to
> the axes with ax.add_artist(arrow).
> 
> I'll be happy to help out with a prototype if you have trouble.  Take
> a look at matplotlib.table.Cell, which John Gill wrote to support
> tables.  You can use this as a simple model for how to write new
> artists (things that draw into a figure) composed of other artists.
> 
> It would be nice to have a fancy arrow class, that supported text
> labeling, at the base, along the stem and at the arrowhead.  You could
> also consider a more sophisticated polygon other than a triangle for
> the arrowhead.
> 
> Finally, if you needed to draw *a lot of arrows*, order of a thousand
> or more (eg for direction fields), a
> matplotlib.collections.PolygonCollection would be the way to go for
> efficiency.
> 
> JDH
> 
> 
> -------------------------------------------------------
> This SF.Net email is sponsored by:
> Sybase ASE Linux Express Edition - download now for FREE
> LinuxWorld Reader's Choice Award Winner for best database on Linux.
> http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click

[Matplotlib-users] gtk backend unused functions

[Steve C. <ste...@ya...>]

The GTK backend defines _quit_after_print_xvfb(*args), show_xvfb(), and
Dialog_MeasureTool(gtk.Dialog). They were used in early versions of
matplotlib before the non-interactive backends became available.

Is there anyone still using these functions?

Regards,
Steve

Re: [Matplotlib-users] How to draw an arrow using matplotlib

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

>>>>> "Chris" == Chris  <Ch...@Fu...> writes:

    Chris> Dear friends, I just start to use matplotlib, which looks
    Chris> quite promising for me. I need to draw a couple of arrows
    Chris> in my 2D plot. Is there a simple way to get it work?

    Chris> Any suggustions are welcome.

I recommend creating an arrow class, derived from matplotlib.artist.Artist, that
contains a matplotlib.lines.Line2D for the arrow stem and a
matplotlib.patches.RegularPolygon  with numVertices=3 for the arrow
head.  You can control the rotation of the arrowhead with the
orientation argument.  

Once you have this class so defined, you can add it instances of it to
the axes with ax.add_artist(arrow).

I'll be happy to help out with a prototype if you have trouble.  Take
a look at matplotlib.table.Cell, which John Gill wrote to support
tables.  You can use this as a simple model for how to write new
artists (things that draw into a figure) composed of other artists.

It would be nice to have a fancy arrow class, that supported text
labeling, at the base, along the stem and at the arrowhead.  You could
also consider a more sophisticated polygon other than a triangle for
the arrowhead.

Finally, if you needed to draw *a lot of arrows*, order of a thousand
or more (eg for direction fields), a
matplotlib.collections.PolygonCollection would be the way to go for
efficiency.

JDH