[Matplotlib-users] dash length for dashed contours

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.

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