format error saving eps figure using custom linestyle

Bug report

Bug summary

When the linestyle is changed from a predefined value to on-off tuple, the resulting figure cannot be saved as eps file format.

Code for reproduction

    import numpy as np
    import matplotlib.pyplot as plt
    x = y = np.linspace(-5, 5)
    x, y = np.meshgrid(x, y)
    z = x**2 + y**2 - 10
    
    plt.rcParams['contour.negative_linestyle'] = [7.0, 7.0]
    f = plt.figure()
    plt.contour(x, y, z, colors='k', levels=20)
    f.savefig('test.eps')

Actual outcome

Traceback (most recent call last):

  File "<ipython-input-12-d73b5c362b1b>", line 1, in <module>
    f.savefig('test.eps')

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\figure.py", line 2180, in savefig
    self.canvas.print_figure(fname, **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_qt5agg.py", line 88, in print_figure
    super().print_figure(*args, **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backend_bases.py", line 2082, in print_figure
    **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 842, in print_eps
    return self._print_ps(outfile, 'eps', *args, **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 871, in _print_ps
    **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 966, in _print_figure
    self.figure.draw(renderer)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\figure.py", line 1709, in draw
    renderer, self, artists, self.suppressComposite)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\image.py", line 135, in _draw_list_compositing_images
    a.draw(renderer)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\axes\_base.py", line 2647, in draw
    mimage._draw_list_compositing_images(renderer, self, artists)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\image.py", line 135, in _draw_list_compositing_images
    a.draw(renderer)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\artist.py", line 38, in draw_wrapper
    return draw(artist, renderer, *args, **kwargs)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\collections.py", line 329, in draw
    self._offset_position)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 492, in draw_path_collection
    offset_position)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backend_bases.py", line 245, in draw_path_collection
    self.draw_path(gc0, path, transform, rgbFace)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 414, in draw_path
    self._draw_ps(ps, gc, rgbFace)

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 759, in _draw_ps
    self.set_linedash(*gc.get_dashes())

  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 276, in set_linedash
    s = "[%s] %d setdash\n" % (_nums_to_str(*seq), offset)

TypeError: %d format: a number is required, not NoneType

Expected outcome

The above snippet works when png extension is used, or when [7.0, 7.0] is replaced with 'dashed'

Matplotlib version

Operating system: windows 7.0
Matplotlib version: 3.1.1
Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
Python version: 3.7.1
Jupyter version (if applicable):
Other libraries:

Funnily, it seems to work fine if you use plt.rcParams['lines.linestyle'] = [7.0, 7.0]. Though this is probably a bug in itself - since it should either make all lines that linestyle, or none of them.

It doesn't! plt.rcParams['lines.linestyle'] = [7.0, 7.0] affects plots not contour lines. For example, the following code throws the same error with what you suggested.

plt.rcParams['lines.linestyle'] = [7.0, 7.0]
f = plt.figure()
plt.plot(np.random.randn(300))
f.savefig('test.eps')

Ok, seems we need to update #11797 with some more cases.

I see a bit clearer now. The linestyles argument of contour also does not take any on-off patern as input. So the fact that it works for some backend is an untested coincidence.

The intended way to change the pattern is via the 'lines.dashed_pattern' parameter. So your code would need to look like this:

import numpy as np
import matplotlib.pyplot as plt
x = y = np.linspace(-5, 5)
x, y = np.meshgrid(x, y)
z = x**2 + y**2 - 10

plt.rcParams['contour.negative_linestyle'] = "dashed"
plt.rcParams['lines.dashed_pattern'] = (7, 1)

f = plt.figure()
plt.contour(x, y, z, colors="k", levels=20)
f.savefig('test.eps')
plt.show()

Pushing to 3.3 as there is a way to avoid this problem and tightening up the API will likely require some careful thought.

This would be fixed by #15828 (which basically mentions this case in the first message re: passing None instead of zero).

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format error saving eps figure using custom linestyle #14996

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format error saving eps figure using custom linestyle #14996

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ImportanceOfBeingErnest commented on Aug 7, 2019

Mahdi-Hosseinali commented on Aug 7, 2019

ImportanceOfBeingErnest commented on Aug 7, 2019

ImportanceOfBeingErnest commented on Aug 8, 2019

tacaswell commented on Sep 1, 2019

anntzer commented on Jan 21, 2020

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