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1. efiring commented on Jun 8, 2011

   

   efiring

   on Jun 8, 2011

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   On 06/08/2011 11:18 AM, astrofrog wrote:

   The following code works:

    import matplotlib as mpl
    mpl.use('Agg')
    import matplotlib.pyplot as plt
   
    fig = plt.figure()
    ax = fig.add_subplot(1, 1, 1)
    ax.contourf([[0.,1.], [1.,0.]], levels=[0.5, 1.0, 2.0])
    fig.savefig('contourf.png')
   

   but if I try and specify a single level, the code crashes:

    import matplotlib as mpl
    mpl.use('Agg')
    import matplotlib.pyplot as plt
   
    fig = plt.figure()
    ax = fig.add_subplot(1, 1, 1)
    ax.contourf([[0.,1.], [1.,0.]], levels=[0.5])
    fig.savefig('contourf.png')
   

   contourf contours between levels, so there is not much it can do with
   a single level. The error (an invalid input) could be trapped at an
   early stage. That sort of input validation is done somewhat erratically
   in mpl. Personally, I don't want to see us try to anticipate every
   possible input error and clutter the code with validation, but some
   types of error are worth trapping.

   Eric

   The exception is:

    Traceback (most recent call last):
      File "test.py", line 7, in<module>
        ax.contourf([[0.,1.], [1.,0.]], levels=[0.5])
      File "/Users/tom/Library/Python/2.6/site-packages/matplotlib/axes.py", line 7403, in contourf
        return mcontour.QuadContourSet(self, *args, **kwargs)
      File "/Users/tom/Library/Python/2.6/site-packages/matplotlib/contour.py", line 1103, in __init__
        ContourSet.__init__(self, ax, *args, **kwargs)
      File "/Users/tom/Library/Python/2.6/site-packages/matplotlib/contour.py", line 719, in __init__
        self.allsegs, self.allkinds = self._get_allsegs_and_allkinds()
      File "/Users/tom/Library/Python/2.6/site-packages/matplotlib/contour.py", line 1136, in _get_allsegs_and_allkinds
        lowers, uppers = self._get_lowers_and_uppers()
      File "/Users/tom/Library/Python/2.6/site-packages/matplotlib/contour.py", line 820, in _get_lowers_and_uppers
        if self.zmin == lowers[0]:
    IndexError: index out of bounds
   
2. astrofrog commented on Jun 8, 2011

   

   astrofrog

   on Jun 8, 2011

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   Ok, that makes sense. One possibility would be that if the length of the levels iterable is 1, one could append +inf as the second value (since that is probably the expected behavior if people try and specify a single value). Just a thought, but feel free to close the ticket without any changes.
3. efiring commented on Jun 16, 2011

   

   efiring

   on Jun 16, 2011

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   Closed with 58c4713. It turns out that a check for 2 or more levels for contourf was already being made, but it was missing the case where the levels were specified via a kwarg. I slight rearrangement fixed that.
4. efiring

   closed this as completedon Jun 16, 2011