matplotlib-users Mailing List for matplotlib (Page 1398)

On Tue, 2004-11-16 at 18:23 -0800, Rich Drewes wrote:
> Hello,
> 
> Several users (including Humufr and Niklas Volbers) have reported on this
> list a compile error building matplotlib with pygtk.  The error looks
> something like this:
> 
> In file included from src/_gtkagg.cpp:8:
>  /usr/include/pygtk-2.0/pygobject.h:124: error: parse error before 
> `typename"
>  /usr/include/pygtk-2.0/pygobject.h:131: error: parse error before 
> `typename"
> 
> I also experienced this problem.  It appears to be some sort of namespace
> collision on the token "typename" (what this is colliding with isn't
> clear).  By changing "typename" to "typname" or some other spelling in
> /usr/include/pygtk-2.0/pygobject.h I was then able to build matplotlib
> successfully.
> 
> If someone knows what is causing this and has a better solution, please
> advise.  Perhaps it has something to do with GCC 3.4.x and that particular
> pygtk release.
> 
> Rich Drewes
The problem is a bug in old versions of PyGTK, upgrading to a later version 
(2.4.1 I believe) will fix it.
Regards
Steve

> 
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Hello,

Several users (including Humufr and Niklas Volbers) have reported on this
list a compile error building matplotlib with pygtk.  The error looks
something like this:

In file included from src/_gtkagg.cpp:8:
 /usr/include/pygtk-2.0/pygobject.h:124: error: parse error before 
`typename"
 /usr/include/pygtk-2.0/pygobject.h:131: error: parse error before 
`typename"

I also experienced this problem.  It appears to be some sort of namespace
collision on the token "typename" (what this is colliding with isn't
clear).  By changing "typename" to "typname" or some other spelling in
/usr/include/pygtk-2.0/pygobject.h I was then able to build matplotlib
successfully.

If someone knows what is causing this and has a better solution, please
advise.  Perhaps it has something to do with GCC 3.4.x and that particular
pygtk release.

Rich Drewes

Hi Chris,

>> Matlab also returns one object- the varargout cell array which is 
>> similar to Python's list or tuple. You write a function, and pack 
>> varargout with nargout results: [a,b]=matlabfun().
>
>
>
> I haven't used Matlab for a while, and not a newer version than 5.*, 
> but  IIRC, while the above notation looks, like you are returning a 
> cell array, you could not call that fun with a single return argument. 
> Perhaps that's changed, in which case you shouldn't use nargout in 
> Matlab either!


Maybe my example wasn't clear. There are good reasons for using 
varargout and nargout in Matlab. If I write a function to fit a peak, I 
can return the position, height, FWHM and sumResiduals along with some 
information about how the peakfitting algorithm concluded. If a user 
calls [p,h,fwhm,sr] = peakfit(x,y), you use nargout to determine that 
the caller does not want the algorithm report.

>
> Anyway, my main point was that kludging a nargout implementation in 
> python was not a good idea. I'd much rather see matplotlib be 
> pythonesque than matlabesque. Perhaps my goals are different than 
> others, but I use Python, rather than Matlab, largely because I like 
> the language better.
>
I originally looked into Python because everyone who works with it loves 
it, and it is free. I felt that the switch could be quick and painless 
because of John and the other MPL developers efforts with the Matlab 
interface. I would probably have waited to switch until after graduating 
if I hadnt googled "Python AND Matlab" one fateful day. (Cornell 
recently sent me a survey asking whether I felt $230 was fair for a 12 
month license!). The matlab interface is already matlabesque. I think 
*args and Matlab's varargin are equivalent. Let me write up some 
examples using nargout as it is intended to be used, and I'll submit 
them to the list in a new thread. This one has strayed a bit from the 
original topic.

Darren

Thanks for your feedback. I ran it with --verbose-helpful, and indeed I 
got some helpful messages (see below). I'll have to remember that in future.

You are right, one module is loading the TKAgg backend, and the other is 
loading the GTK backend.

The reason I have this in my modules is that I have one module A which 
is intended to be very general purpose, but has a couple of hooks to do 
plots. Module A doesn't care which backend it uses, and at the moment it 
uses the matplotlib.matlab interface because that's what I knew when I 
wrote it.

Module B is a more specific application, which was using matlab calls, 
but I found I had to convert it to use GTK and the matplotlib API 
because I call it from application C which has a GUI window using GTK 
and glade.

Summary:

module A: general purpose, matlab API, no hardcoded backend

module B: more specialised, matplotlib API, GTK backend, explicit GTK 
window management

app C: more specialised, no matplotlib or matlab, GTK & glade GUI, 
functions from modules A and B used in callback threads

I don't really want to force module A to use GTK, because TKAgg (or 
whatever's in .matplotlibrc) is more likely to work for other users on 
other machines. So for the moment I can get by, if I import module A 
after module B.

But maybe there is some nice way to do things that I'm missing. Perhaps 
I can convert module A to use the matplotlib API but still not specify 
the backend, and it will still work standalone and also start playing 
nicely with module B and app C. I'll have a play with it when I get some 
time.

Here is the output from "python frog.py --verbose-helpful":

$ python frog.py --verbose-debug
matplotlib data path c:\Python23\share\matplotlib
loaded rc file c:\Python23\share\matplotlib\.matplotlibrc
matplotlib version 0.64
verbose.level debug
interactive is False
numerix Numeric 23.3
font search path ['c:\\Python23\\share\\matplotlib', 
'/usr/share/fonts/msttf']
loaded ttfcache file M:\home\mra\.ttffont.cache
matplotlib data path c:\Python23\share\matplotlib
loaded rc file c:\Python23\share\matplotlib\.matplotlibrc
matplotlib version 0.64
verbose.level debug
interactive is False
backend TkAgg version 8.4
Could not load matplotlib icon: Couldn't recognize the image file format 
for file 'c:\Python23\share\matplotlib\matplotlib.svg'
Traceback (most recent call last):
   File "frog.py", line 6, in ?
     embedding_in_gtk2_mra.plotme()
   File "M:\home\My Documents\My 
Downloads\matplotlib-0.64\matplotlib-0.64\exampl 
                                es\embedding_in_gtk2_mra.py", line 43, 
in plotme
     toolbar = NavigationToolbar(canvas, win)
   File 
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line 
                                                        963, in __init__
     NavigationToolbar2.__init__(self, canvas)
   File "C:\Python23\Lib\site-packages\matplotlib\backend_bases.py", 
line 786, in                                                        __init__
     self._init_toolbar()
   File 
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line 
                                                        1028, in 
_init_toolbar
     self._init_toolbar2_4()
   File 
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line 
                                                        1091, in 
_init_toolbar2_4
     parent=self.win,)
   File 
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line 
                                                        1423, in __init__
     self.IMAGE_FORMAT         = 
matplotlib.backends.backend_mod.IMAGE_FORMAT
AttributeError: 'module' object has no attribute 'IMAGE_FORMAT'

Cheers,
Matthew.

John Hunter wrote:
>>>>>>"matthew" == matthew arnison <ma...@ca...> writes:
> 
> 
>     matthew> Oh dear. I'm going to take another u-turn, and say I hit
>     matthew> this IMAGE_FORMAT attribute glitch again.
> 
> Try running your script with --verbose-helpful or --verbose-debug and
> report the output.  That way we can see what is happening behind the
> scenes.
> 
>     matthew> To atone for my reversals, I have isolated a test case,
>     matthew> and I attach sample code. It seems to be triggered by
>     matthew> importing matplotlib.matlab in one module, and importing
>     matthew> matplotlib backend stuff directly in another module.
> 
>     matthew> Running frog.py gives:
>     matthew> line 1423, in __init__ self.IMAGE_FORMAT =
>     matthew> matplotlib.backends.backend_mod.IMAGE_FORMAT
>     matthew> AttributeError: 'module' object has no attribute
>     matthew> 'IMAGE_FORMAT'
> 
> Fernando added the backend_mod to matplotlib.backends.__init__.py --
> perhaps he has some insight into what is going on.
> 
>     matthew> As commented in the code, changing the order of the
>     matthew> import statements in frog.py avoids the bug. Or using the
>     matthew> workaround I mentioned below.
> 
>     matthew> Hmmm. Now I remember an email from John Hunter saying
>     matthew> that pythonic matplotlib should not be mixed with the
>     matthew> matlab interface. Maybe this glitch is an artefact of
>     matthew> that. It does mean however that all my modules have to
>     matthew> use one API or the other.
> 
> Yes, this is basically undefined.  When using the API, you control
> figure canvases, windows, backends, etc, independently.  When you
> import matplotlib.matlab, it parses your rc file (or not finding it
> falls back on a default) and may try and load a different backend.
> Since IMAGE_FORMAT is only used in some backends, my guess is you are
> seeing a backend conflict.  Running --verbose-helpful should give you a
> clue about which backends matplotlib is loading.
> 
> Note there are scant few features in the matlab interface that you
> can't access directly from the API.  There is no compelling reason to
> mix them, save laziness, and as you are finding, it doesn't really
> save you any time.  If you want to use something from the matlab
> interface and aren't sure how to do it from the API, open up matlab.py
> and take a look at how that function does it.  A large number if not
> the majority of matlab interface functions simply forward their calls
> on to the current axes.
> 
> JDH

Hi All,

Can anyone tell me how to change the size of the legend produced by
matlab.legend independently of my axis tick labels?

lh=legend(['a','b','c'],loc=4,fontsize=8)

doesn't work and there seems to be nothing in the lh object that would
help.

Cheers,
Cory

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

    Chris> Dear John, I see your points. However, after I changed to
    Chris> using add_artist. This is still nothing on the canvas. I
    Chris> think that there is some problem with the draw function of
    Chris> my arrow class. I have no idea what else should be
    Chris> there. At the moment, only one call in my case as below.

    Chris> 	def draw(self, renderer): self._stem.draw(renderer)

    Chris> Could u tell what else should be called?

Your drawing function looks fine.  Could this be a problem with axes
limits.  Make sure the x and y limits are set properly with the xlim,
ylim or axis commands.  The limits are normally autoscaled by calling
plot, but you are not using it so you have to take care that the
limits are set.  After you get a working prototype, I can help you
with the autoscaling part.

If this doesn't fix your problem, email me your matlab.py, axes.py and
test code as attachments off-list and I'll take a look.

JDH

Darren Dale wrote:

> Matlab also returns one object- the varargout cell array which is 
> similar to Python's list or tuple. You write a function, and pack 
> varargout with nargout results: [a,b]=matlabfun().

I haven't used Matlab for a while, and not a newer version than 5.*, but 
  IIRC, while the above notation looks, like you are returning a cell 
array, you could not call that fun with a single return argument. 
Perhaps that's changed, in which case you shouldn't use nargout in 
Matlab either!

Anyway, my main point was that kludging a nargout implementation in 
python was not a good idea. I'd much rather see matplotlib be 
pythonesque than matlabesque. Perhaps my goals are different than 
others, but I use Python, rather than Matlab, largely because I like the 
language better.

-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...

Dear John,

I see your points. However, after I changed to using add_artist. This is 
still nothing on the canvas. I think that there is some problem with the 
draw function of my arrow class. I have no idea what else should be 
there. At the moment, only one call in my case as below.

	def draw(self, renderer):
		self._stem.draw(renderer)

Could u tell what else should be called?

Best regards,
Chris

John Hunter wrote:
>>>>>>"Chris" == Chris  <bi...@Fu...> writes:
> 
> 
>     Chris> I tried with what you suggested to make an Arrow class. To
>     Chris> begin with, I only put an Line2D instance. I searched for
>     Chris> table stuff in axes.py, matlab.py to make the arrow
>     Chris> importable from matplotlib.matlab. Then I also try a very
>     Chris> very simple demo and I expect to see a simple
>     Chris> line. However, I can not see it. Could someone tell me what
>     Chris> is the problem. Here is my very very rudimental codes.
> 
> Nowhere in your code do you actually draw the arrows in self.arrows.
> In Axes.draw you would need to do
> 
>     for arrow in self.arrows: 
>         arrow.draw(renderer)
> 
> And this should work.
> 
> However, you can avoid all the overhead of add_arrow, and keeping a
> list of arrows in self.arrows simply by doing
> 
> 
>      def arrow(self, x, y, *args, **kwargs):
>          a = Arrow(x,y, *args, **kwargs)
>          self.add_artist(a)
>                  ^^^
>          return a
> 
> Ie, call add_artist which is a generic method for adding artists to
> the axes.
> 
> Hope this helps,
> JDH
> 
> 
> 
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>>>>> "Chris" == Chris  <bi...@Fu...> writes:

    Chris> I tried with what you suggested to make an Arrow class. To
    Chris> begin with, I only put an Line2D instance. I searched for
    Chris> table stuff in axes.py, matlab.py to make the arrow
    Chris> importable from matplotlib.matlab. Then I also try a very
    Chris> very simple demo and I expect to see a simple
    Chris> line. However, I can not see it. Could someone tell me what
    Chris> is the problem. Here is my very very rudimental codes.

Nowhere in your code do you actually draw the arrows in self.arrows.
In Axes.draw you would need to do

    for arrow in self.arrows: 
        arrow.draw(renderer)

And this should work.

However, you can avoid all the overhead of add_arrow, and keeping a
list of arrows in self.arrows simply by doing


     def arrow(self, x, y, *args, **kwargs):
         a = Arrow(x,y, *args, **kwargs)
         self.add_artist(a)
                 ^^^
         return a

Ie, call add_artist which is a generic method for adding artists to
the axes.

Hope this helps,
JDH

I tried with what you suggested to make an Arrow class. To begin with, I 
only put an Line2D instance. I searched for table stuff in axes.py, 
matlab.py to make the arrow importable from matplotlib.matlab. Then I 
also try a very very simple demo and I expect to see a simple line. 
However, I can not see it. Could someone tell me what is the problem. 
Here is my very very rudimental codes.

-----------------------------------------------------------------
arrow.py

from artist import Artist
from lines import Line2D
from patches import RegularPolygon

class Arrow(Artist):
	"""
	An arrow with an triangular head .

	"""
	def __init__(self, xdata=None, ydata=None, *args, **kwargs):
		
		Artist.__init__(self)
		print xdata, ydata
		self._stem = Line2D(xdata, ydata, *args, **kwargs)
		
	def draw(self, renderer):
		self._stem.draw(renderer)

------------------------------------------------------------
in file axes.py
   in function cla add:
         self.arrows = []
---------------------------
     def add_arrow(self, a):
         'Add an arrow instance to the list of axes arrows'
         self._set_artist_props(a)
         self.arrows.append(a)

     def arrow(self, x, y, *args, **kwargs):
         a = Arrow(x,y, *args, **kwargs)
         self.add_arrow(a)
         return a
-------------------------------------------------------------
in file matlab.py
	add two tring for importing arrow
-------------------------------------------------------------
arrow_demo.py

from matplotlib.matlab import *

x = [0,1]
y = [0,1]
arrow(x,y, color='b',linestyle='-')
show()
-------------------------------------------------------------

Best regards,
Chris

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

    matthew> Oh dear. I'm going to take another u-turn, and say I hit
    matthew> this IMAGE_FORMAT attribute glitch again.

Try running your script with --verbose-helpful or --verbose-debug and
report the output.  That way we can see what is happening behind the
scenes.

    matthew> To atone for my reversals, I have isolated a test case,
    matthew> and I attach sample code. It seems to be triggered by
    matthew> importing matplotlib.matlab in one module, and importing
    matthew> matplotlib backend stuff directly in another module.

    matthew> Running frog.py gives:
    matthew> line 1423, in __init__ self.IMAGE_FORMAT =
    matthew> matplotlib.backends.backend_mod.IMAGE_FORMAT
    matthew> AttributeError: 'module' object has no attribute
    matthew> 'IMAGE_FORMAT'

Fernando added the backend_mod to matplotlib.backends.__init__.py --
perhaps he has some insight into what is going on.

    matthew> As commented in the code, changing the order of the
    matthew> import statements in frog.py avoids the bug. Or using the
    matthew> workaround I mentioned below.

    matthew> Hmmm. Now I remember an email from John Hunter saying
    matthew> that pythonic matplotlib should not be mixed with the
    matthew> matlab interface. Maybe this glitch is an artefact of
    matthew> that. It does mean however that all my modules have to
    matthew> use one API or the other.

Yes, this is basically undefined.  When using the API, you control
figure canvases, windows, backends, etc, independently.  When you
import matplotlib.matlab, it parses your rc file (or not finding it
falls back on a default) and may try and load a different backend.
Since IMAGE_FORMAT is only used in some backends, my guess is you are
seeing a backend conflict.  Running --verbose-helpful should give you a
clue about which backends matplotlib is loading.

Note there are scant few features in the matlab interface that you
can't access directly from the API.  There is no compelling reason to
mix them, save laziness, and as you are finding, it doesn't really
save you any time.  If you want to use something from the matlab
interface and aren't sure how to do it from the API, open up matlab.py
and take a look at how that function does it.  A large number if not
the majority of matlab interface functions simply forward their calls
on to the current axes.

JDH

Oh dear. I'm going to take another u-turn, and say I hit this
IMAGE_FORMAT attribute glitch again.

To atone for my reversals, I have isolated a test case, and I attach
sample code. It seems to be triggered by importing matplotlib.matlab in
one module, and importing matplotlib backend stuff directly in another
module.

Running frog.py gives:

Traceback (most recent call last):
    File "frog.py", line 4, in ?
      embedding_in_gtk2_mra.plotme()
    File "M:\home\My Documents\My
Downloads\matplotlib-0.64\matplotlib-0.64\examples\embedding_in_gtk2_mra.py", 

line 39, in plotme
      toolbar = NavigationToolbar(canvas, win)
    File
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line
963, in __init__
      NavigationToolbar2.__init__(self, canvas)
    File "C:\Python23\Lib\site-packages\matplotlib\backend_bases.py",
line 786, in __init__
      self._init_toolbar()
    File
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line
1028, in _init_toolbar
      self._init_toolbar2_4()
    File
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line
1091, in _init_toolbar2_4
      parent=self.win,)
    File
"C:\Python23\lib\site-packages\matplotlib\backends\backend_gtk.py", line
1423, in __init__
      self.IMAGE_FORMAT         =
matplotlib.backends.backend_mod.IMAGE_FORMAT
AttributeError: 'module' object has no attribute 'IMAGE_FORMAT'

As commented in the code, changing the order of the import statements in
frog.py avoids the bug. Or using the workaround I mentioned below.

Hmmm. Now I remember an email from John Hunter saying that pythonic
matplotlib should not be mixed with the matlab interface. Maybe this
glitch is an artefact of that. It does mean however that all my modules
have to use one API or the other.

Cheers,
Matthew.

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.
> 
> 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.

John Hunter wrote:

>>>>>>"Chris" == Chris Barker <Chr...@no...> writes:
>>>>>>            
>>>>>>
>
>
>    Chris> no, I was a bit wrong. Python functions always return one
>    Chris> object, and when it appears that you are returning multiple
>    Chris> objects, you are really returning a single tuple with
>    Chris> multiple objects in it. Have I got it right this time?
>
>Sounds right to me.  Your answer does point to the danger of using
>nargout in python
>
>  ret = somefunc()
>  i,j = ret  
>
>If somefunc is relying on nargout, it will botch it.
>
>I think the only sane use for nargout in python is in auto-conversion
>scripts, and then with appropriate warnings. 
>
>Thanks said, I would still like to have it, for that reason.
>  
>
Matlab also returns one object- the varargout cell array which is 
similar to Python's list or tuple. You write a function, and pack 
varargout with nargout results: [a,b]=matlabfun().

Well it works now.

For other reasons I downgraded to 0.63 and upgraded again to 0.64. As part
of this I found I had to manually wipe not only
Python23/Lib/site-packagaes/matplotlib but also Python23/share/matplotlib
to avoid errors (e.g. an ImportError: cannot import artist from Artist).

But now I don't need that workaround to avoid the IMAGE_FORMAT error.
examples/embedding_in_gtk2.py works fine too, after patching in the

toolbar = NavigationToolbar(canvas, win)

API change.

I'm sorry for the confusion.

Cheers,
Matthew.

On Wed, 10 Nov 2004, Steve Chaplin wrote:

> 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

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


    Chris> no, I was a bit wrong. Python functions always return one
    Chris> object, and when it appears that you are returning multiple
    Chris> objects, you are really returning a single tuple with
    Chris> multiple objects in it. Have I got it right this time?

Sounds right to me.  Your answer does point to the danger of using
nargout in python

  ret = somefunc()
  i,j = ret  

If somefunc is relying on nargout, it will botch it.

I think the only sane use for nargout in python is in auto-conversion
scripts, and then with appropriate warnings. 

Thanks said, I would still like to have it, for that reason.

JDH

John Hunter wrote:

> What do you mean that python functions always return a tuple?  How
> about functions that return an int, or a string, or whatever?  

> 
>>>>def func(): return 1
>>>>type(func())
> 
> <type 'int'>
> 
> Do you mean that python functions that return tuples always return
> tuples <wink> ?

no, I was a bit wrong. Python functions always return one object, and 
when it appears that you are returning multiple objects, you are really 
returning a single tuple with multiple objects in it. Have I got it 
right this time?

-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...

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

    Chris> Darren Dale wrote:
    >> >I guess there is no way in Python of emulating >Matlab"s
    >> detection of the number of output arguments.  I just got a
    >> response from c.l.p. Somebody remembered seeing this at ASPN:
    >> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742
    >> expecting() is the workhorse, equivalent to Matlab's nargout:

    Chris> Very cool. but I'd caution against using it. I'd much
    Chris> rather see matplotlib be pythonesque than an exact
    Chris> duplicate of MATLAB. This is NOT pythonesque!

I tend to agree with the caution against using it.  But it would be
useful in some contexts, like converting existing matlab m-files to
python/numeric/numarray, the desire for which has occurred in some
contexts.  Last time the discussion came up, the lack of nargout was
raised as a problem for any converter code.


    Chris> Precisely speaking, python functions ALWAYS return just one
    Chris> object: A tuple. That tuple can contain any number of other
    Chris> objects, and sequence unpacking means it can look like
    Chris> you're returning multiple values, but you're not
    Chris> really. i.e.

What do you mean that python functions always return a tuple?  How
about functions that return an int, or a string, or whatever?  

>>> def func(): return 1
>>> type(func())
<type 'int'>

Do you mean that python functions that return tuples always return
tuples <wink> ?

JDH

Darren Dale wrote:
>  >I guess there is no way in Python of emulating
>  >Matlab"s detection of the number of output arguments.
> 
> I just got a response from c.l.p. Somebody remembered seeing this at ASPN:
> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742
> 
> expecting() is the workhorse, equivalent to Matlab's nargout:

Very cool. but I'd caution against using it. I'd much rather see 
matplotlib be pythonesque than an exact duplicate of MATLAB. This is NOT 
pythonesque!

Precisely speaking, python functions ALWAYS return just one object: A 
tuple. That tuple can contain any number of other objects, and sequence 
unpacking means it can look like you're returning multiple values, but 
you're not really. i.e.

def test():
	return (1,2,3) # same as return 1,2,3

# now call it:

a,b,c = test()
(a,b,c) = test()
x = test(); a,b,c = x
x = test(); a = x[0]; b = x[1]; c = x[2]

# Are all equivalent

if one uses the last two forms, expecting() will break.

-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...

Hi John,

>     >> I guess there is no way in Python of emulating Matlab"s
>     >> detection of the number of output arguments.
>
>     Darren> I just got a response from c.l.p. Somebody remembered
>     Darren> seeing this at ASPN:
>     Darren> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742
>
>     Darren> expecting() is the workhorse, equivalent to Matlab's
>     Darren> nargout:
>
>     Darren> import inspect,dis
>
> Hi Darren,
>
> Wow, I didn't know this was possible in python.  Does it work under
> python2.2?

The ASPN page says it has been tested on 2.3.3. I dont have a 2.2 installation 
handy to check it.

>
> Perhaps you would like to write up nargin and nargout function with
> some doc strings and send them my way?  I could add them to the matlab
> interface.  But we need to make sure they are 2.2 compliant.

I will give it a shot in my free time, but without getting into it, my next 
month is pretty full.

>
> As an aside, do we need nargout to make "find" work like matlab's?
> Isn't it enough just to check the shape of the input array and
> processing it one way for 1D arrays and another way for 2D arrays?
>

The problem is that mlab.find() is currently a thin wrapper around a numeric 
or numarray method, which only works for 1D arrays. ravelling the arrays 
passed to find would make it easy to continue using the method called by 
find(), but I had trouble figuring out how to process the 1xM results of that 
method back into an NxM or MxN array that could be used to index an N-D 
array.  

It would be nice to be able to address Numeric and numarray with a single 
index. Matlab does this. For example, if a=array([[1,2],[3,4]]), a[0] would 
be 1, a[1] would be 3 (Matlab's convention, again if memory serves.) 

-- 

Darren

>>>>> "Darren" == Darren Dale <dd...@co...> writes:

    >> I guess there is no way in Python of emulating Matlab"s
    >> detection of the number of output arguments.

    Darren> I just got a response from c.l.p. Somebody remembered
    Darren> seeing this at ASPN:
    Darren> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742

    Darren> expecting() is the workhorse, equivalent to Matlab's
    Darren> nargout:

    Darren> import inspect,dis

Hi Darren,

Wow, I didn't know this was possible in python.  Does it work under
python2.2?

Perhaps you would like to write up nargin and nargout function with
some doc strings and send them my way?  I could add them to the matlab
interface.  But we need to make sure they are 2.2 compliant.

As an aside, do we need nargout to make "find" work like matlab's?
Isn't it enough just to check the shape of the input array and
processing it one way for 1D arrays and another way for 2D arrays?
 
Cheers,
JDH

>>>>> "Jos=E9" =3D=3D Jos=E9 Alexandre Nalon <na...@te...> writes:

    Jos=E9> Hello, I think I've found a bug in mathtext - sorry if this
    Jos=E9> appeared before, I couldn't find it in the list archives.

    Jos=E9> When I try:

    Jos=E9> xlabel(r"$-(\Omega_a^' + \Omega_a)$")

    Jos=E9> I don't get what I expected. The label shows -\Omega_a and
    Jos=E9> stops there. Further tests showed that, whenever I try a
    Jos=E9> single quote in a mathtext string, the text is not rendered
    Jos=E9> from the quote on.

    Jos=E9> This might not be a bug, I might be doing something
    Jos=E9> wrong. If this is the case, please tell me how to do it
    Jos=E9> right.

I don't believe your use of ' is valid TeX.  Try
Omega_a^\prime

    Jos=E9> Thanks in advance.

Sure thing,
JDH

> xlabel(r"$-(\Omega_a^' + \Omega_a)$")
>
> I don't get what I expected. The label shows -\Omega_a and stops
> there. Further tests showed that, whenever I try a single quote
> in a mathtext string, the text is not rendered from the quote on.
>
> This might not be a bug, I might be doing something wrong. If
> this is the case, please tell me how to do it right.
>

try replacing ^' with ^\prime

Darren

Hello,

I think I've found a bug in mathtext - sorry if this appeared
before, I couldn't find it in the list archives.

When I try:

xlabel(r"$-(\Omega_a^' + \Omega_a)$")

I don't get what I expected. The label shows -\Omega_a and stops
there. Further tests showed that, whenever I try a single quote
in a mathtext string, the text is not rendered from the quote on.

This might not be a bug, I might be doing something wrong. If
this is the case, please tell me how to do it right.

Thanks in advance.

---
José Alexandre Nalon
na...@te...

 >I guess there is no way in Python of emulating
 >Matlab"s detection of the number of output arguments.

I just got a response from c.l.p. Somebody remembered seeing this at ASPN:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/284742

expecting() is the workhorse, equivalent to Matlab's nargout:

import inspect,dis

def expecting():
    """Return how many values the caller is expecting"""
    f = inspect.currentframe()
    f = f.f_back.f_back
    c = f.f_code
    i = f.f_lasti
    bytecode = c.co_code
    instruction = ord(bytecode[i+3])
    if instruction == dis.opmap['UNPACK_SEQUENCE']:
        howmany = ord(bytecode[i+4])
        return howmany
    elif instruction == dis.opmap['POP_TOP']:
        return 0
    return 1

def cleverfunc():
    howmany = expecting()
    if howmany == 0:
        print "return value discarded"
    if howmany == 2:
        return 1,2
    elif howmany == 3:
        return 1,2,3
    return 1

def test():
    cleverfunc()
    x = cleverfunc()
    print x
    x,y = cleverfunc()
    print x,y
    x,y,z = cleverfunc()
    print x,y,z

test()

Hi Jouni,

Jouni K Sepp=E4nen wrote:

>On Sun, 14 Nov 2004 18:08:59 +0200, Jouni K Sepp=E4nen
><jou...@gm...> wrote:
> =20
>
>>Here's what I'm using to emulate Matlab's find; it only seems to work
>>with Numeric, not numarray
>>   =20
>>
>
>Oops - actually it seems that after
>
>from matplotlib.numerix import ravel, indices, compress
>
>the function works whether numerix is using numarray or Numeric.
>
>Making a special case of single-dimensional inputs is not very
>elegant, but doing otherwise would break compatibility with the
>existing mlab.find; and I guess there is no way in Python of emulating
>Matlab's detection of the number of output arguments.
> =20
>

I looked at this a while back, and came to the same conclusion. Thats an=20
interesting question, can Python determine the number of output=20
arguments? I dont know of a convenient function call, but it seems like=20
that information must exist somewhere. I'll ask at c.l.p.

Darren