Re: [Matplotlib-users] dash length for dashed contours

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

On 2013/01/22 11:50 PM, Andrew Dawson wrote:
> Hi all,
>
> [TL;DR: is it possible to control the length of the dashes in dashed
> contours, if so how?]
>
> I'd like to be able to control the length of dashes for dashed contours.
> My motivation is that I'm making a contour plot that uses dashes for the
> negative contours, and the plot needs to be a specific (small) size for
> the particular journal, so the small size of the plot makes the dashes
> look rather long and is a problem for some tight contours.
>
> I have tried using some a dashes-style argument for the linestyles
> keyword of contour but I can't get it to work (although I appreciate it
> is not documented as something one can do). For example I tried:
>
>      import matplotlib.pyplot as plt
>      import numpy as np
>      x = y = np.linspace(-np.pi, np.pi, 100)
>      X, Y = np.meshgrid(x, y)
>      Z = np.sin(X) * np.cos(Y)
>      plt.contour(x, y, Z, linestyles=[(3, 3)])
>      plt.show()
>
> This fails at the point where I show (or save, doesn't matter which
> backend) the plot with a PyCXX error:
>
>      TypeError: PyCXX: Error creating object of type
> N2Py7SeqBaseINS_6ObjectEEE from 3
>
> I've fiddled with several other styles of argument and all fail in a
> similar way.

There seems to be a nasty tangle of bugs and obsolete documentation 
here.  It should be perfectly simple and straightforward, but it isn't.

https://github.com/matplotlib/matplotlib/issues/1701

Eric

>
> What I'd like to know is: is it possible to control the dash length of
> dashed contours at all? It seems like it should be as one can do this
> with lines easy enough. I looked through the code, and a dashes-style
> argument seems to get passed through the stack correctly, but fails when
> the Collection is drawn. It would be a really nice feature if this could
> be implemented in matplotlib.
>
> Thanks,
> Andrew
>
>
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