Re: [Matplotlib-users] switching output formats within a function

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

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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