matplotlib-devel Mailing List for matplotlib

Andrew Straw wrote:
> I was thinking I want an exact a replica of the wx API as possible,
well, I'm a big fan of wx.Sizers, but we all know that they confuses folks.
Given that grid-like layouts are likely to be the most common with MPL, 
maybe just make a GridBagSizer, and forget the rest? All the other 
sizers are just a simplification of that anyway.
just my 0ドル.2
Despite that small suggestion -- very nice work!
-Chris
-- 
Christopher Barker, Ph.D.
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Seattle, WA 98115 (206) 526-6317 main reception
Chr...@no...

Hi Ken,
Thanks for your comments.
Ken McIvor wrote:
>1. It appears that as_sizer_element() uses the _axes_sizer_elements 
>dictionary to cache MplAxesSizerElement instances. Using a 
>WeakKeyDictionary from the "weakref" module instead of a regular 
>dictionary may be necessary to allow the garbage collection of the 
>MplAxesSizerElements when their associated Axes gets GC'd.
> 
>
I'll check into this.
>2. Convenience MplBoxSizer subclasses that let you omit the "orient" 
>keyword might be nice:
>
> class MplHBoxSizer(MplBoxSizer):
> def __init__(self):
> MplBoxSizer.__init__(self, orientation='vertical')
> 
>
I was thinking I want an exact a replica of the wx API as possible,
simply so my feeble mind doesn't get (more) confused. Is there anything
like this in stock wx? I think it's a decent enough idea, but I'd rather
not cause namespace bloat. But, if you're really into it, let's do it.
>3. Couldn't you just drop mplsizer.py into the "matplotlib.toolkits" 
>virtual package? Maybe you can't -- I'm pretty new to applied python- 
>eggery.
> 
>
I think this is possible, and I hope for not too much effort. This is
the result of historic accident and personal time-allocation issues.
Mplsizer started life as a private setuptools-ized package, and I'm not
spending my time to de-setuptools-ize software -- I see setuptools as
the way forward, not something (I will spend my time) to remove. I
understand that some people aren't too fond of setuptools, and to them,
I say, "patches welcome".
>4. I feel we should avoid the whole European/American spelling 
>problem that WX has. Why not make both 'align_centre' and 
>'align_center' do the same thing?
> 
>
Same answer as to point 2...
>5. Why not use shorter names, with less redundancy? (e.g. 
>"matplotlib.toolkits.sizer", FigureSizer, Box, HBox, Grid, etc)
> 
>
Same answer as to point 2... (I'd be happy to drop the "Mpl" prefix,
though.)

>>>>> "JIM" == JIM MacDonald <ji...@ji...> writes:
 JIM> My second problem involved the resolutions of the image. I'd
 JIM> like to preserve the resolution of my image in the PS output,
 JIM> but I can't figure out how to stop the image being resized
 JIM> and interpolated. Obviously you need to do this for the
There are two kinds of images in matplotlib -- AxesImage and
FigureImage. By definition, the AxesImage is interpolated to fit into
the Axes box. You can control the aspect ratio of the interpolation,
but it will be interpolated. FigureImage, on the other hand, performs
a pixel dump to the postscript canvas at the location you tell it to
-- see examples/figimage_demo.py. It should like you are more
interested in the latter.
If the figure image doesn't work for you, describe your use-case in
some detail and why neither work and we'll see if we can accommodate
it.
JDH

> I don't think this is a problem with the postscript backend. You're rescaling
> the image in your script. Try something like this:
>
> from pylab import *
>
> rc('text', usetex=True)
> rc('ps', usedistiller="xpdf")
>
> figure(1,figsize=(6, 4))
> im=imread('image.png')
> imshow(im,interpolation='nearest')#,extent=[0.98, 20, 0.01, 0.5])
> #axis('normal');
> savefig('image.eps')
I just tried that and it still rescales the image, this time to
243x230. I've found I can use the figsize kwarg to control the
resolution of the embedded image, but of course this means I can't
have the figure the size I want it.
JIM
---

> Would you post an example where the ps2pdf flags make a big difference on the
> output? I just tried with the above png, but I cant tell the difference
> between the results with/without the new flags.
http://jimmacdonald.co.uk/matplotlib/MPD_SinPulse_g0.500.png
JIM
---

On Mon, Jul 31, 2006 at 10:19:46AM -0400, Darren Dale wrote:
> I see. Thanks for pointing this out and providing the solution. The fla=
gs you=20
> suggested are passed to ps2pdf as of svn 2639.
 Great ! Thanks.
 I like open source software so much because of these little details
:->.
--=20
 Ga=EBl

On Monday 31 July 2006 10:05, Gael Varoquaux wrote:
> On Mon, Jul 31, 2006 at 10:01:23AM -0400, Darren Dale wrote:
> > Would you post an example where the ps2pdf flags make a big difference on
> > the output? I just tried with the above png, but I cant tell the
> > difference between the results with/without the new flags.
>
> Last image of http://scipy.org/GaelVaroquaux, the example script. You
> can also have a look at the "pylab2pdf2 script, where I use
> environmental variables to get a proper behaviour from GS and avoid this
> problem.
I see. Thanks for pointing this out and providing the solution. The flags you 
suggested are passed to ps2pdf as of svn 2639.
Darren

On Mon, Jul 31, 2006 at 10:01:23AM -0400, Darren Dale wrote:
> Would you post an example where the ps2pdf flags make a big difference =
on the=20
> output? I just tried with the above png, but I cant tell the difference=
=20
> between the results with/without the new flags.
Last image of http://scipy.org/GaelVaroquaux, the example script. You
can also have a look at the "pylab2pdf2 script, where I use
environmental variables to get a proper behaviour from GS and avoid this
problem.
--=20
 Ga=EBl

Great. Thanks John.
There was one other thing I forgot to mention.
I added two lines (+comment) in the backend_wx.py to select the
Pan/Zoom tool by default.
If you don't like that, then obviously just leave those lines out,
But I find that pan/zoom is what I want to do 90% of the time, and
zoom is the other 10%. "No tool" is what I want pretty much 0% of the
time (is there some use for no-tool mode that I'm missing?)
--bb
On 7/31/06, John Hunter <jdh...@ac...> wrote:
> >>>>> "Bill" == Bill Baxter <wb...@gm...> writes:
>
> Bill> Ok. Such a pain though... Are whole files acceptable
> Bill> instead of diffs? It's relatively easy to do a windiff or
>
> Multiple contributions per patch are fine, just do like you did and
> list what is in them. If there is an objection to part of the patch,
> you may be asked to resubmit w/o the controversial parts, but if all
> the changes look good the whole thing can go in. And we prefer svn
> diffs over individual files.
>
> Ken, would you like to be added to the devel list to handle some of
> these patches. Just email me your sf id if so.
>
> JDH
>

On Monday 31 July 2006 09:32, JIM MacDonald wrote:
> > I'll look into this soon. I'm hesitant to add another rc option, maybe we
> > can consider using these settings as the defaults. I'll post again after
> > I have had a chance to play with it.
>
> Defaulting to lossless FlateEncode compression seems like a good idea,
> if the file is too big you can always run another distill cycle after
> wards manually.
>
> Another possibility would be to set the option based on the format of
> the image loaded (I'm sure I read somewhere that it is planned to
> support formats other than PNG). ie FlateEncode for GIF's and PNG's
> and DCTEncode for JPEG's.
[...]
> Sure,
> http://jimmacdonald.co.uk/matplotlib/image.png
> http://jimmacdonald.co.uk/matplotlib/image.eps
> http://jimmacdonald.co.uk/matplotlib/image.py
>
> image.py generates image.eps from image.png. image.png is simple
> enough for ps2pdf not to use DCT encoding. Looking at the postscript
> shows that the image has resolution of 335x230 compared to the
> original of 318x301.
Would you post an example where the ps2pdf flags make a big difference on the 
output? I just tried with the above png, but I cant tell the difference 
between the results with/without the new flags.
Darren

On Monday 31 July 2006 09:32, JIM MacDonald wrote:
> > The resolution for Postscript is 72 dpi, and I'm not sure this can be
> > changed. Would you send me an example postscript file along with the
> > original png?
>
> Sure,
> http://jimmacdonald.co.uk/matplotlib/image.png
> http://jimmacdonald.co.uk/matplotlib/image.eps
> http://jimmacdonald.co.uk/matplotlib/image.py
>
> image.py generates image.eps from image.png. image.png is simple
> enough for ps2pdf not to use DCT encoding. Looking at the postscript
> shows that the image has resolution of 335x230 compared to the
> original of 318x301.
I don't think this is a problem with the postscript backend. You're rescaling 
the image in your script. Try something like this: 
from pylab import *
rc('text', usetex=True)
rc('ps', usedistiller="xpdf")
figure(1,figsize=(6, 4))
im=imread('image.png')
imshow(im,interpolation='nearest')#,extent=[0.98, 20, 0.01, 0.5])
#axis('normal');
savefig('image.eps')
Darren

> I'll look into this soon. I'm hesitant to add another rc option, maybe we can
> consider using these settings as the defaults. I'll post again after I have
> had a chance to play with it.
Defaulting to lossless FlateEncode compression seems like a good idea,
if the file is too big you can always run another distill cycle after
wards manually.
Another possibility would be to set the option based on the format of
the image loaded (I'm sure I read somewhere that it is planned to
support formats other than PNG). ie FlateEncode for GIF's and PNG's
and DCTEncode for JPEG's.
> The resolution for Postscript is 72 dpi, and I'm not sure this can be changed.
> Would you send me an example postscript file along with the original png?
Sure,
http://jimmacdonald.co.uk/matplotlib/image.png
http://jimmacdonald.co.uk/matplotlib/image.eps
http://jimmacdonald.co.uk/matplotlib/image.py
image.py generates image.eps from image.png. image.png is simple
enough for ps2pdf not to use DCT encoding. Looking at the postscript
shows that the image has resolution of 335x230 compared to the
original of 318x301.
JIM
---

>>>>> "Eric" == Eric Firing <ef...@ha...> writes:
 Eric> return newtrans if not units == 'inches': raise
 Eric> ValueError('units must be dots or inches') if fig is None:
This all looks great and I like the interface. My only suggestions is
to add points (1/72. inches) since this is commonly used throughout
matplotlib, is easy, and is the most common distance metric used in
graphics.
 Eric> Minimal testing and illustration of the use of offsets is
 Eric> now in examples/transoffset.py. It includes cartesian and
 Eric> polar coordinates.
 
Excellent!
JDH

>>>>> "Bill" == Bill Baxter <wb...@gm...> writes:
 Bill> Ok. Such a pain though... Are whole files acceptable
 Bill> instead of diffs? It's relatively easy to do a windiff or
Multiple contributions per patch are fine, just do like you did and
list what is in them. If there is an objection to part of the patch,
you may be asked to resubmit w/o the controversial parts, but if all
the changes look good the whole thing can go in. And we prefer svn
diffs over individual files.
Ken, would you like to be added to the devel list to handle some of
these patches. Just email me your sf id if so.
JDH

John,
I will respond to the more philosophical parts of your message later.
I have committed changes to _transforms.* and transforms.py along the 
lines of your suggestions for a quick improvement to the ease of drawing 
with offsets.
> The best way may be for the extension code to provide a shallowcopy
> method and require derived transform classes to implement it. All
> references will be preserved, but a new object will be created.
> 
> We only need this for SeparableTransformation and
> NonseparableTransformation but the methods will also have to be
> defined virtually in the base classes.
> 
> We have to think about what should be preserved in the shallow
> copies. For the use case at hand, we want to preserve the references
> to the values but not the offset transform.
> 
I think I got this right--or at least as right as the existing deepcopy 
methods--but it would be good if you, or another c++ wizard, could take 
a look. The way I have it seems to work as intended, but testing has 
been light, and I don't really know c++. I have never written any from 
scratch, only modified existing code.
> I'm not so sure that deepcopy is really needed. I can't think of a
> use case off hand.
I think it is needed for pickling, but I suspect that the screwiness of 
the objects that the _transforms module produces would prevent pickling 
in any case. Other than that, I don't see any point in the deepcopy 
methods, or the corresponding (and redundant) deepcopy functions in 
transforms.py. I marked with comments a block that I think should be 
excised from transforms.py.
The convenience function I came up with is transforms.offset_copy:
def offset_copy(trans, fig=None, x=0, y=0, units='inches'):
 '''
 Return a shallow copy of a transform with an added offset.
 args:
 trans is any transform
 kwargs:
 fig is the current figure; it can be None if units are 'dots'
 x, y give the offset in units of 'inches' or 'dots'
 units is 'inches' or 'dots'
 '''
 newtrans = trans.shallowcopy()
 if units == 'dots':
 newtrans.set_offset((x,y), identity_transform())
 return newtrans
 if not units == 'inches':
 raise ValueError('units must be dots or inches')
 if fig is None:
 raise ValueError('For units of inches a fig kwarg is needed')
 tx = Value(x) * fig.dpi
 ty = Value(y) * fig.dpi
 newtrans.set_offset((0,0), translation_transform(tx, ty))
 return newtrans
Minimal testing and illustration of the use of offsets is now in 
examples/transoffset.py. It includes cartesian and polar coordinates.
Eric

Is it possible to add another level to the axes rc parameters, so the x and y 
axes can be controlled independently.
axes.xaxis.*
axes.yaxis.*
I am happy to add this feature if people think this is a good addition.
Cheers,
Malte.

On 7/31/06, Ken McIvor <mc...@ii...> wrote:
> On Jul 30, 2006, at 8:07 AM, Bill Baxter wrote:
> > I went ahead and implemented this yesterday on a long plane flight.
> > The changed files (backend_bases.py, and widgets.py) are attached to
> > the above tracker entry. Also I changed backend_wx.py to grab the
> > mouse generally when you click on the graphs, so that panning and such
> > continues to track even when you go outside the window. Similar
> > changes should probably also be made to the other backends too.
>
> This sounds like it could be a pretty stellar improvement to the WX
> backend. Thanks!
Just to be clear, the only thing that applies to wx specifically is
that I made the wx backend grab the system pointer on mouse down and
release it on mouse up. (Basically just a change of 4 lines of code
-- two CaptureMouse() calls and two ReleaseMouse() calls). The rest
is GUI independent and should benefit all GUI backends.
>
> I should be at a work-related meeting on Tuesday with Matt Newville,
> the WX backend maintainer. I'll try to get some time set aside to
> get your changes merged on my laptop before them, so that we can
> check them out properly afterward. My big concern is to investigate
> how these changes may affect people who are embedding WxAgg figures
> in wxPython applications. If you've done what I think you have, that
> shouldn't be a problem.
Definitely more people should test it and review the code. It works
for me, but maybe there are some things I haven't thought of. Like
I've never tried embedding. But I don't think this should cause
problems there. On the other hand, the widget-level grabbing
infrastructure might have problems with a GUI back-end that doesn't do
system-level grabbing. For instance you start dragging on a Slider,
drag off the window, and let go. If you aren't doing system level
grabbing then you won't ever get the mouse up to tell you that you
should release the widget-level mouse grab.
> > I also added get_value methods to the CheckButtons and RadioButtons,
> > because it didn't seem like there was any good way to get that info.
>
> You may want to submit this portion of the changes as a separate
> patch. I've found that my patches get accepted faster when I only do
> one thing per patch.
Ok. Such a pain though... Are whole files acceptable instead of
diffs? It's relatively easy to do a windiff or whatever to look over
the changes and accept or reject line by line. (In fact Robert
Osfield who quite ably runs the OpenSceneGraph project feels so
strongly about it that he *only* allows patches to be submitted as
complete files so he can easilly use a visual diff tool to merge
changes).
> > Finally I don't really get what the deal is with the Slider's
> > "closedmin"/"closedmax" options.
>
> Sorry, I can't help you with this one.
>
> > Please let me know if there's a better way/place to submit patches.
>
> I've always done exactly what you're doing now: uploading it on SF
> then emailing the developers' list.
Ok. Thanks.
--Bill

Hi Ken,
Thanks for the reply.
On 7/31/06, Ken McIvor <mc...@ii...> wrote:
> On Jul 24, 2006, at 9:16 PM, Bill Baxter wrote:
> > I think all these problems could be fixed if the display interface
> > were turned into a separate process that communicates with the Python
> > program using pipes or some other IPC mechanism. I used this
> > technique in a (C/C++) image debugging utility program I wrote
> > (http://www.billbaxter.com/projects/imdebug) and it works quite well.
>
> The biggest problem I see with this approach is that matplotlib has a
> "display list" drawing model (as opposed to the "big matrix of
> pixels" model). An example of what I mean is that when someone
> resizes a {Gtk,Tk,Wx}Agg figure, the entire plot is re-rendered from
> scratch to the new pixel dimensions. It could be a failure of
> imagination, but I can't see how you could move the display interface
> to a subprocess without moving the rest of matplotlib along with it.
> I just can't see a clear line along which to separate out the "graph
> display server" part.
What's the problem with sending the "display list" or with having most
of matplotlib also exist in the separate process? As long as
evaluating that display list doesn't involve making extensive
callbacks into user code, then it shouldn't be a problem. Having
matplotlib live on both sides of the process boundary is ok in my
opinion, because it can be made to work that way. But having to have
the *users's* app on both sides is a problem. Or having to do so many
RPC callbacks back to users' code that a single rendering becomes
intolerably slow.
Conceptually, in terms of the "clear line", I think maybe a special
'axes' class would get you a lot of what is needed. That would act
like a proxy for 'axes' actually living in another process.
Anyway, clearly matplotlib shouldn't always use remote display. If
you're using for embedded graphing then that would be silly. It would
be more for general interactive use and debugging purposes.
> > Has anyone given thought to making matplotlib work in such a manner?
> > It would be hell to do in C or C++ I think, but with Python's
> > extensive RPC libs I bet it wouldn't be so bad.
>
> Python has extensive RPC libraries?!?! ;-)
Heh, well compared to C++ at least. :-) My only experience with it
was with doing some very simple operations using xmlrpc. But compared
with how hard that would have been for me to do in C++ I was
impressed.
> The point of this long-winded email is that you probably could build
> some kind of RPC system to run matplotlib remotely, but I believe it
> would be an awful lot of work. In terms of manhours, my opinion is
> that you'd come out ahead if you just focused on debugging your
> current problems.
Ok. It's good to know practically the best way to achieve "good
enough" but I like to think and discuss about how to achieve "best
possible", also. :-)
Regards
--bb

On Jul 30, 2006, at 8:07 AM, Bill Baxter wrote:
> I went ahead and implemented this yesterday on a long plane flight.
> The changed files (backend_bases.py, and widgets.py) are attached to
> the above tracker entry. Also I changed backend_wx.py to grab the
> mouse generally when you click on the graphs, so that panning and such
> continues to track even when you go outside the window. Similar
> changes should probably also be made to the other backends too.
This sounds like it could be a pretty stellar improvement to the WX 
backend. Thanks!
I should be at a work-related meeting on Tuesday with Matt Newville, 
the WX backend maintainer. I'll try to get some time set aside to 
get your changes merged on my laptop before them, so that we can 
check them out properly afterward. My big concern is to investigate 
how these changes may affect people who are embedding WxAgg figures 
in wxPython applications. If you've done what I think you have, that 
shouldn't be a problem.
> I also added get_value methods to the CheckButtons and RadioButtons,
> because it didn't seem like there was any good way to get that info.
You may want to submit this portion of the changes as a separate 
patch. I've found that my patches get accepted faster when I only do 
one thing per patch.
> Finally I don't really get what the deal is with the Slider's
> "closedmin"/"closedmax" options.
Sorry, I can't help you with this one.
> Please let me know if there's a better way/place to submit patches.
I've always done exactly what you're doing now: uploading it on SF 
then emailing the developers' list.
Ken

Andrew,
This looks very cool, and I'm looking forward to playing around with 
it. Thanks for the hard work!
Shooting from the hip, here are some initial comments. I may be able 
to submit patches for some of the more innocuous items later in the 
week.
1. It appears that as_sizer_element() uses the _axes_sizer_elements 
dictionary to cache MplAxesSizerElement instances. Using a 
WeakKeyDictionary from the "weakref" module instead of a regular 
dictionary may be necessary to allow the garbage collection of the 
MplAxesSizerElements when their associated Axes gets GC'd.
2. Convenience MplBoxSizer subclasses that let you omit the "orient" 
keyword might be nice:
 class MplHBoxSizer(MplBoxSizer):
 def __init__(self):
 MplBoxSizer.__init__(self, orientation='vertical')
3. Couldn't you just drop mplsizer.py into the "matplotlib.toolkits" 
virtual package? Maybe you can't -- I'm pretty new to applied python- 
eggery.
4. I feel we should avoid the whole European/American spelling 
problem that WX has. Why not make both 'align_centre' and 
'align_center' do the same thing?
5. Why not use shorter names, with less redundancy? (e.g. 
"matplotlib.toolkits.sizer", FigureSizer, Box, HBox, Grid, etc)
Ken

On Thu, Jul 27, 2006 at 01:33:42PM +0100, JIM MacDonald wrote:
> Another way to do it is to pass extra
> command line options to ps2pdf (-dAutoFilterColorImages=3Dfalse
> -sColorImageFilter=3DFlateEncode should do it for colour images). I
> thought embedding it in the PS file would be more flexible.
 +1 for that. I am having exactly the same problem.
--=20
 Ga=EBl

On Jul 24, 2006, at 9:16 PM, Bill Baxter wrote:
> I think all these problems could be fixed if the display interface
> were turned into a separate process that communicates with the Python
> program using pipes or some other IPC mechanism. I used this
> technique in a (C/C++) image debugging utility program I wrote
> (http://www.billbaxter.com/projects/imdebug) and it works quite well.
The biggest problem I see with this approach is that matplotlib has a 
"display list" drawing model (as opposed to the "big matrix of 
pixels" model). An example of what I mean is that when someone 
resizes a {Gtk,Tk,Wx}Agg figure, the entire plot is re-rendered from 
scratch to the new pixel dimensions. It could be a failure of 
imagination, but I can't see how you could move the display interface 
to a subprocess without moving the rest of matplotlib along with it. 
I just can't see a clear line along which to separate out the "graph 
display server" part.
> Has anyone given thought to making matplotlib work in such a manner?
> It would be hell to do in C or C++ I think, but with Python's
> extensive RPC libs I bet it wouldn't be so bad.
Python has extensive RPC libraries?!?! ;-)
In seriousness, RPC is an acknowledged weakness of Python's standard 
library. For example, Python gives you a sockets API that is much 
nicer to use than the BSD sockets API or WinSock, but which still 
makes you worry about all of the platform-specific idiosyncrasies of 
socket programming. It's my understanding that this is one of the 
big reasons Twisted came into being.
As another example, before Python 2.4 added the "subprocess" module, 
there was no portable way to spawn and communicate with 
subprocesses... you'd have to worry about the shell of whatever 
platform you were on mangling the commandline, you couldn't reliably 
interrupt subprocesses on win32 (no os.kill() to send a SIGINT with), 
etc.
The point of this long-winded email is that you probably could build 
some kind of RPC system to run matplotlib remotely, but I believe it 
would be an awful lot of work. In terms of manhours, my opinion is 
that you'd come out ahead if you just focused on debugging your 
current problems. I suspect that the matplotlib developers and 
irregular contributers like myself will more able to help with that 
debugging than we would be able to help with writing a display 
server... but please don't think that I'm speaking for everyone!
Ken

I submitted an enhancement request to the Sourceforge bug list about
grabbing behavior in the GUI-independent widgets.
http://sourceforge.net/tracker/index.php?func=detail&aid=1530104&group_id=80706&atid=560720
I went ahead and implemented this yesterday on a long plane flight.
The changed files (backend_bases.py, and widgets.py) are attached to
the above tracker entry. Also I changed backend_wx.py to grab the
mouse generally when you click on the graphs, so that panning and such
continues to track even when you go outside the window. Similar
changes should probably also be made to the other backends too.
I also added get_value methods to the CheckButtons and RadioButtons,
because it didn't seem like there was any good way to get that info.
Finally I don't really get what the deal is with the Slider's
"closedmin"/"closedmax" options. These don't seem very useful to me
(namely the =False variety). If it meant the max was actually
max-[machine epsilon] then ok, but it's implemented as "don't set the
value if it would get set to the max" i.e. how close you get to the
max/min depends on how patient you are carefully moving the mouse to
the end of the slider. Which is just frustrating to me. It's hard to
make it go "as high as it will go".
Please let me know if there's a better way/place to submit patches.
--bb

On 7/30/06, Andrew Straw <str...@as...> wrote:
> The basic
> idea is to create a layout engine for matplotlib. Not wanting to
> (re-)invent an API, I decided simply to imitate the layout engine I knew
> best, which is wxPython.
Very cool!

>>>>> "Eric" == Eric Firing <ef...@ha...> writes:
 Eric> John, I think we really need copy (and maybe deepcopy)
 Eric> functions that work with all transforms, not just Separable
 Eric> transforms. This looks fairly easy except for one thing:
 Eric> the transform creation functions return objects that don't
 Eric> provide any clean way of distinguishing among the types of
 Eric> transform. type(trans) reports <type 'Affine'>, regardless
I've seen this, I thinki it's a problem with pycxx but am not sure
 Eric> of what kind of transform it really is. I have not been
 Eric> able to figure out where this is coming from. One can't
 Eric> cleanly use hasattr(funcxy) to detect a Nonseparable
 Eric> transform because all transforms have the attribute, whether
 Eric> they use it or not. I could use "try: trans.get_funcxy()"
Again, this is a problem with pycxx. You cannot do inheritance where
B and C inherit some methods from A unless all methods are in A, B and
C. It's ugly but that is the way it is for now. So I define all the
methods in the base class and raise if they are not available.
Unfortunately, pycxx is not actively developed so I doubt this will
change .
 Eric> and catch the exception, but that is ugly. (And the second
 Eric> time I tried it, it hung ipython.)
 Eric> I suspect you have thought about this already--do you have
 Eric> any suggested solutions? Is there at least a simple way to
 Eric> get type(trans) to work right? From the code it looks like
 Eric> it should, so there appears to be a bug in the code or in
 Eric> cxx.
The best way may be for the extension code to provide a shallowcopy
method and require derived transform classes to implement it. All
references will be preserved, but a new object will be created.
We only need this for SeparableTransformation and
NonseparableTransformation but the methods will also have to be
defined virtually in the base classes.
We have to think about what should be preserved in the shallow
copies. For the use case at hand, we want to preserve the references
to the values but not the offset transform.
I'm not so sure that deepcopy is really needed. I can't think of a
use case off hand.
As I respond, I wonder if we are applying the right solution to the
wrong problem. I think these changes are worth doing because they are
easy and work with the existing code and are useful. But in the
longer run, I think the offsets, while useful, can be better
accomplished by developing a transform chain as Jouni suggested.
Normal affine multiplication doesn't work since the transformations
may be nonlinear. But we should be able to do something like (here in
python but this would probably be in the extension code)
class CompositeTransform:
 def __init__(self, transforms):
 self._transforms = transforms
 def xy_tup(self, xy):
 for transform in self._transforms:
 xy = transform.xy_tup(xy)
 return xy
Removing the offset transforms would break internal and external code,
but would probably be a cleaner solution in the long run.
JDH