savefig crashes in backend_p[df|s].py when using plot-option mew

[juisoo]

Debian Wheezy
Python 2.7.3
matplotlib 1.1.1rc2

I have a simple plot with a marker which I want to save to PDF/EPS with savefig. When setting the markeredgewidth I get an Error from savefig or rather backend_pdf.py. The same holds for eps export. Here's the traceback (MWE for this behaviour below):
Traceback (most recent call last):
File "mwe.py", line 13, in
fig.savefig('mmo_example_1.pdf',format='pdf')
File "/usr/lib/pymodules/python2.6/matplotlib/figure.py", line 1185, in savefig
self.canvas.print_figure(_args, *_kwargs)
File "/usr/lib/pymodules/python2.6/matplotlib/backend_bases.py", line 2021, in print_figure
*_kwargs)
File "/usr/lib/pymodules/python2.6/matplotlib/backend_bases.py", line 1789, in print_pdf
return pdf.print_pdf(_args, **kwargs)
File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_pdf.py", line 2191, in print_pdf
file.close()
File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_pdf.py", line 482, in close
self.writeMarkers()
File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_pdf.py", line 1212, in writeMarkers
bbox = bbox.padded(lw * 0.5)
TypeError: can't multiply sequence by non-int of type 'float'

# python

import numpy as np
import matplotlib as mpl
import matplotlib.pyplot as plt

t = np.arange(-0.9999, 0.0, 0.001)

fig = plt.figure(figsize=(7.,5.))
ax = fig.add_axes([0.13,0.13,0.82,0.82])

ax.plot(t,0.2*np.sin(4*t)+t + np.sign(t)*0.5,'r-o',mfc='white',mec='r',mew='1',markevery=(500,1000)) # produces the following errror when using savefig:
#  File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_pdf.py", line 1212, in writeMarkers
#    bbox = bbox.padded(lw * 0.5)
#TypeError: can't multiply sequence by non-int of type 'float'

#ax.plot(t,0.2*np.sin(4*t)+t + np.sign(t)*0.5,'r-o',mfc='white',mec='r',markevery=(500,1000))  # works like a charm

plt.draw()

fig.savefig('mmo_example_1.eps',format='eps')
fig.savefig('mmo_example_1.pdf',format='pdf')

plt.show()

[jenshnielsen]

That is a very old version of Matplotlib. Could you please try with a newer version. Preferably the latest release candidate of 1.4.0

[juisoo]

Well, yes, it is indeed. However, it's the most current there is for Debian Wheezy (packaged). As I don't have sudo or root permissions on my machine and have no idea how to install it locally and then import it, I would need a little nudge in the right direction.
Anyway I figured, it might be less hassle for someone with a current version to run the MWE and check if the problem persists.

[juisoo]

Note that the Error message and traceback for eps export differ slightly from the pdf-ones posted above:

Traceback (most recent call last):
  File "mwe.py", line 21, in <module>
    fig.savefig('mmo_example_1.eps',format='eps')
  File "/usr/lib/pymodules/python2.6/matplotlib/figure.py", line 1185, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/backend_bases.py", line 2021, in print_figure
    **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/backend_bases.py", line 1784, in print_eps
    return ps.print_eps(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_ps.py", line 954, in print_eps
    return self._print_ps(outfile, 'eps', *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_ps.py", line 987, in _print_ps
    **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_ps.py", line 1080, in _print_figure
    self.figure.draw(renderer)
  File "/usr/lib/pymodules/python2.6/matplotlib/artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/figure.py", line 898, in draw
    func(*args)
  File "/usr/lib/pymodules/python2.6/matplotlib/artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/axes.py", line 1997, in draw
    a.draw(renderer)
  File "/usr/lib/pymodules/python2.6/matplotlib/artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/matplotlib/lines.py", line 556, in draw
    rgbFace)
  File "/usr/lib/pymodules/python2.6/matplotlib/backends/backend_ps.py", line 589, in draw_markers
    ps_cmd.append('%.1f setlinewidth' % lw)
TypeError: float argument required, not str

[TAC edited to add mark up]

[jenshnielsen]

I think that the issue is that mew should be the integer 1 not the string '1'
For some reason the string works in the display backend but not the pdf and eps backends.

[jenshnielsen]

The doc string says

markeredgewidth or mew: float value in points

So you can replace integer with float in the above.

[juisoo]

Thanks Jens! That was it.
In the meanwhile I learned how to install python modules locally. And, yes, the "problem" persists in 1.4.x.
Now this could be closed marked "Not a bug", however, IMO, this behaviour (working in display but not in pdf/ps backend) violates the principle of least surprise.
I would suggest therefore to make the display backend more strict in only accepting number values and/or throw an exception or at least a warning when when passing a string value to option mew

[jenshnielsen]

Agreed there is scope for improving the validation of input parameters to plot et. al.

[tacaswell]

I suspect that someplace in the agg layer there is a (maybe implicit) cast to float involved in going down to c++, whereas in this case the value is being thrown (un-validated) at a string formatter or being used in multiplication.