Re: [Matplotlib-users] Issue with hist plotting

[Eric F. <ef...@ha...>]

On 08/14/2010 04:47 AM, Daπid wrote:
> Hello.
>
> I have had an issue trying to plot an histogram with Matplotlib. The line is:
>
> plt.hist([SNIa.angles, SNIbc.angles, SNII.angles], 11, range=[-pi, pi],
>           normed=True,histtype='stepfilled',color=['g', 'r',
> 'b'],alpha=[1, 0.6, 1])

The problem is that the "alpha" kwarg can never be other than a scalar 
in mpl at present, as far as I know.  The error message from to_rgba was 
intended to be informative, but in this case it is misleading.

If you want different alpha values for your different bars, you will 
have to use a list of rgba values for your color kwarg, and leave out 
the alpha kwarg.  You can construct the list like this (untested):

from matplotlib.colors import colorConverter

colors = [colorConverter.to_rgba(c, a) for c, a in zip(['g', 'r', 'b'], 
[1, 0.6, 1]]

Eric

>
> But the error is raised when I try to save the image. For completness,
> the  whole program is here:
> http://nopaste.voric.com/paste.php?f=8zl9i4
>
> If I call hist as stated above, I get the following error report:
>
> Traceback (most recent call last):
>    File "C:\Documents and
> Settings\David\Escritorio\Python\IAYC\Supernovae\final\Deprecated\supernovae_bug.py",
> line 35, in<module>
>      plt.savefig('angular_merged_1bis.png')
>    File "C:\Python25\Lib\site-packages\matplotlib\pyplot.py", line 363,
> in savefig
>      return fig.savefig(*args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\figure.py", line
> 1084, in savefig
>      self.canvas.print_figure(*args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\backend_bases.py",
> line 1886, in print_figure
>      **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\backends\backend_agg.py",
> line 438, in print_png
>      FigureCanvasAgg.draw(self)
>    File "C:\Python25\Lib\site-packages\matplotlib\backends\backend_agg.py",
> line 394, in draw
>      self.figure.draw(self.renderer)
>    File "C:\Python25\Lib\site-packages\matplotlib\artist.py", line 55,
> in draw_wrapper
>      draw(artist, renderer, *args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\figure.py", line 798, in draw
>      func(*args)
>    File "C:\Python25\Lib\site-packages\matplotlib\artist.py", line 55,
> in draw_wrapper
>      draw(artist, renderer, *args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\axes.py", line 1934, in draw
>      a.draw(renderer)
>    File "C:\Python25\Lib\site-packages\matplotlib\artist.py", line 55,
> in draw_wrapper
>      draw(artist, renderer, *args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\patches.py", line 366, in draw
>      r, g, b, a = colors.colorConverter.to_rgba(self._facecolor, self._alpha)
>    File "C:\Python25\Lib\site-packages\matplotlib\colors.py", line 353,
> in to_rgba
>      raise ValueError('to_rgba: Invalid rgba arg "%s"\n%s' % (str(arg), exc))
> ValueError: to_rgba: Invalid rgba arg "[ 0.   0.5  0.   1. ]"
> alpha must be in range 0-1
>
>
>
> If I delete the color declaring, I get instead:
>
> Traceback (most recent call last):
>    File "C:\Documents and
> Settings\David\Escritorio\Python\IAYC\Supernovae\final\Deprecated\supernovae_bug.py",
> line 35, in<module>
>      plt.savefig('angular_merged_1bis.png')
>    File "C:\Python25\Lib\site-packages\matplotlib\pyplot.py", line 363,
> in savefig
>      return fig.savefig(*args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\figure.py", line
> 1084, in savefig
>      self.canvas.print_figure(*args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\backend_bases.py",
> line 1886, in print_figure
>      **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\backends\backend_agg.py",
> line 438, in print_png
>      FigureCanvasAgg.draw(self)
>    File "C:\Python25\Lib\site-packages\matplotlib\backends\backend_agg.py",
> line 394, in draw
>      self.figure.draw(self.renderer)
>    File "C:\Python25\Lib\site-packages\matplotlib\artist.py", line 55,
> in draw_wrapper
>      draw(artist, renderer, *args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\figure.py", line 798, in draw
>      func(*args)
>    File "C:\Python25\Lib\site-packages\matplotlib\artist.py", line 55,
> in draw_wrapper
>      draw(artist, renderer, *args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\axes.py", line 1934, in draw
>      a.draw(renderer)
>    File "C:\Python25\Lib\site-packages\matplotlib\artist.py", line 55,
> in draw_wrapper
>      draw(artist, renderer, *args, **kwargs)
>    File "C:\Python25\Lib\site-packages\matplotlib\patches.py", line 383, in draw
>      renderer.draw_path(gc, tpath, affine, rgbFace)
>    File "C:\Python25\Lib\site-packages\matplotlib\backends\backend_agg.py",
> line 117, in draw_path
>      self._renderer.draw_path(gc, path, transform, rgbFace)
> TypeError: float() argument must be a string or a number
>
> And works fine without alpha statement. Any change in the other
> arguments does not make any difference on the behaviour.
>
> If I run it from the IDLE, once I get an error, I continue getting it
> even if the problematic part is fixed, until I restart the program. I
> am running Matplotlib 1.0.0 y Python 2.5 sobre WXP.
>
> I haven't find any reference to this in the documentation, so it seems
> to be a bug.
>
>
>
> Regards,
>
> David.
>
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