matplotlib-users Mailing List for matplotlib

On Mon, 5 Jan 2004, John Hunter wrote:
> >>>>> "matthew" == matthew arnison <ma...@ca...> writes:
> 
> matthew> The matplotlib docs say you need to specify the backend
> matthew> before importing matplotlib.matlab. But this seems a bit
> matthew> restrictive: what if I want to display a plot on screen,
> matthew> and then output the same plot to postscript and print it?
> matthew> Normally imports are done only once at the top of a file,
> matthew> but I'd like to be able to switch backends anywhere.
> 
> But there is no reason you shouldn't be able to create a PS figure or
> a GD figure to save. I've been meaning to add a 'PS' extension
> checker in the savefig command that would enable you to save to PS
> from any backend.
> 
> Is this primarily what you need to switch backends for?
Yes that's the sweet spot.
Presumably the Save button on the GTK/WX GUI just calls savefig()? In 
which case you'd be able to save postscript from there too, which would 
be popular too I think.
Another thing that would be handy is a simple cross-platform recipe (or
function call?) for spawning persistent plot windows that don't block
execution of the calling script. It may have been on this list (I should 
really search before asking) but it should be in the matplotlib docs I 
think.
Oh yeah, and a default keyboard shortcut (or three! Esc, Q, Ctrl-Q) for
quitting the plot window.
And, being able to put the legend outside the plot area (either within a 
subplot, or outside all the subplots if the legend is the same for all). A 
big legend tends to cover up the data.
Cheers,
Matthew.

>>>>> "matthew" == matthew arnison <ma...@ca...> writes:
 matthew> The matplotlib docs say you need to specify the backend
 matthew> before importing matplotlib.matlab. But this seems a bit
 matthew> restrictive: what if I want to display a plot on screen,
 matthew> and then output the same plot to postscript and print it?
 matthew> Normally imports are done only once at the top of a file,
 matthew> but I'd like to be able to switch backends anywhere.
The reason you need to specify the backend first is because everything
from making a figure window to mapping an RGB tuple to a color is
backend dependent. The matlab interface wouldn't know what to do with
the 'figure' command without knowing its backend.
What I think would be useful would be able to instantiate any backend
figure with a figure instance from another backend. Eg a backend
factory which did something like
 figPS = backend_factory(fig, 'PS')
 figGD = backend_factory(fig, 'GD')
Ie, you could initialize a figure in any backend with an instance from
another figure.
This probably will never work perfectly across all backends, primarily
because the GTK and WX backends both have a mainloop that they enter
and it would be difficult to run both at the same time (though perhaps
possible with GUI thread). But in most cases you wouldn't want too.
But there is no reason you shouldn't be able to create a PS figure or
a GD figure to save. I've been meaning to add a 'PS' extension
checker in the savefig command that would enable you to save to PS
from any backend.
Is this primarily what you need to switch backends for?
John Hunter

>>>>> "Steve" == Steve Chaplin <ste...@ya...> writes:
 Steve> The problem seems to be that process_docs.py is expecting
 Steve> to read many "matplotlib.*.html" files, but these files do
 Steve> not exist.
Yep, this is a doc bug in the README file. You need to first build the
class docs from the matplotlib root
 > make htmldocs
This will build all the matplotlib html class docs in the 'docs'
subdir, which process_docs.py assumes are there. If all you want are
the class docs, this is all you will need to do. process_docs and the
rest of the files in htdocs build the matplotlib web site.
I've updated the README file -- thanks for letting me know.
JDH

Well I just answered my own question. As the docs point out, you can use 
the -dPS option to turn on the postscript backend. So to use this in 
harmony with my scripts I needed to:
a) break out the plotting into a separate application called using command
line options (conveniently I had already done this)
b) tell my option parser about the -d option:
import matplotlib
from matplotlib.matlab import *
# ...
def main():
 # ...
 parser.add_option("-d", dest="plotbackend", default="GTK",
 choices=matplotlib._knownBackends.keys(),
 help="Graphics backend to use to generate plots.")
 # ...
c) use options.plotbackend in my own code to tell whether to 
savefig('something.ps')
It's a bit awkward, but workable.
Cheers,
Matthew.
On Mon, 5 Jan 2004, matthew arnison wrote:
> Hi
> 
> I'm writing a small script to plot my data, and I'd like to use a command 
> line option to allow the same plot to be either displayed with GTK or 
> output to postscript.
> 
> This means I have to switch matplotlib backends within the script.
> 
> Now by the time I know what option the user has chosen, I'm in a function:
> 
> def plotThings(options):
> matplotlib.use(options.plotbackend)
> from matplotlib.matlab import *
> 
> plot(...)
> ...
> 
> and python complains
> 
> SyntaxWarning: import * only allowed at module level
> 
> It still works, but I think I'm on thin ice. And it doesn't work if I do:
> 
> def main():
> # ... parse options ...
> 
> matplotlib.use(options.plotbackend)
> from matplotlib.matlab import *
> 
> plotThings(options)
> 
> SyntaxWarning: import * only allowed at module level
> NameError: global name 'plot' is not defined
> 
> The matplotlib docs say you need to specify the backend before importing 
> matplotlib.matlab. But this seems a bit restrictive: what if I want to 
> display a plot on screen, and then output the same plot to postscript and 
> print it? Normally imports are done only once at the top of a file, but 
> I'd like to be able to switch backends anywhere.
> 
> What are your thoughts on this issue?
> 
> I've been using matplotlib for a while. It's the best python plotting tool 
> I reckon. Thanks for contributing to free software.
> 
> Cheers and thanks,
> Matthew.
> 
> 
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Hi
I'm writing a small script to plot my data, and I'd like to use a command 
line option to allow the same plot to be either displayed with GTK or 
output to postscript.
This means I have to switch matplotlib backends within the script.
Now by the time I know what option the user has chosen, I'm in a function:
def plotThings(options):
 matplotlib.use(options.plotbackend)
 from matplotlib.matlab import *
 plot(...)
 ...
and python complains
SyntaxWarning: import * only allowed at module level
It still works, but I think I'm on thin ice. And it doesn't work if I do:
def main():
 # ... parse options ...
 matplotlib.use(options.plotbackend)
 from matplotlib.matlab import *
 plotThings(options)
SyntaxWarning: import * only allowed at module level
NameError: global name 'plot' is not defined
The matplotlib docs say you need to specify the backend before importing 
matplotlib.matlab. But this seems a bit restrictive: what if I want to 
display a plot on screen, and then output the same plot to postscript and 
print it? Normally imports are done only once at the top of a file, but 
I'd like to be able to switch backends anywhere.
What are your thoughts on this issue?
I've been using matplotlib for a while. It's the best python plotting tool 
I reckon. Thanks for contributing to free software.
Cheers and thanks,
Matthew.