Question

Hej,

I’m using the latest version (1.2.0) of matplotlib distributed with macports. I run into an AssertionError (I guess stemming from internal test) running this code

#!/usr/bin/env python

import numpy as np
import matplotlib.pyplot as plt

X,Y = np.meshgrid(np.arange(0, 2*np.pi, .2), np.arange(0, 2*np.pi, .2))
U = np.cos(X)
V = np.sin(Y)

Q = plt.quiver(U, V)
plt.quiverkey(Q, 0.5, .9, 1., 'Label')

plt.gca().add_patch(plt.Circle((10, 10), 1))
plt.savefig('test.pdf')

Three parts of this code are required for me to reproduce the error:

1. The quiver plot has to have a key created with quiver key
2. have to add an additional patch to the current axes
3. I have to save the figure as a PDF (I can display it just fine)

The bug is not dependent on the backend. The traceback I get reads

Traceback (most recent call last):
  File "./test_quiver.py", line 15, in <module>
    plt.savefig('test.pdf')
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/pyplot.py", line 472, in savefig
    return fig.savefig(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/figure.py", line 1363, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 2093, in print_figure
    **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 1845, in print_pdf
    return pdf.print_pdf(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backends/backend_pdf.py", line 2301, in print_pdf
    self.figure.draw(renderer)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/artist.py", line 54, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/figure.py", line 999, in draw
    func(*args)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/artist.py", line 54, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/axes.py", line 2086, in draw
    a.draw(renderer)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/artist.py", line 54, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/quiver.py", line 306, in draw
    self.vector.draw(renderer)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/artist.py", line 54, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/collections.py", line 755, in draw
    return Collection.draw(self, renderer)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/artist.py", line 54, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/collections.py", line 259, in draw
    self._offset_position)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backends/backend_pdf.py", line 1548, in draw_path_collection
    output(*self.gc.pop())
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/matplotlib/backends/backend_pdf.py", line 2093, in pop
    assert self.parent is not None
AssertionError

In case it’s important: I’m on Mac OS X 10.7.5, using python 2.7.3 and matplotlib 1.2.0. Do you also get this error? Is it a bug in matplotlib? Is it system dependent? Is there some workaround?

Answer 1

You can save as eps or svg and convert to pdf. I found that the best way to produce small pdf files is to save as eps in matplotlib and then use epstopdf.

svg also works fine, you can use Inkscape to convert to pdf. A side-effect of svg is that the text is converted to paths (no embedded fonts), which might be desirable in some circumstances.