FIX: fix afm + py3k + logscale

Followed suggestion of @pgnub

Closes matplotlib#3473

Adds test coverage for afm handling

lib/matplotlib/mathtext.py

@@ -1034,7 +1034,7 @@ def __init__(self, default_font_prop):
         if filename is None:
             filename = findfont('Helvetica', fontext='afm',
                                 directory=self.basepath)
-        with open(filename, 'r') as fd:
+        with open(filename, 'rb') as fd:
             default_font = AFM(fd)
         default_font.fname = filename
 

lib/matplotlib/tests/test_backend_ps.py

@@ -23,14 +23,18 @@
     "This test needs a TeX installation")
 
 
-def _test_savefig_to_stringio(format='ps'):
+def _test_savefig_to_stringio(format='ps', use_log=False):
     buffers = [
         six.moves.StringIO(),
         io.StringIO(),
         io.BytesIO()]
 
     plt.figure()
-    plt.plot([0, 1], [0, 1])
+
+    if use_log:
+        plt.yscale('log')
+
+    plt.plot([1, 2], [1, 2])
     plt.title("Déjà vu")
     for buffer in buffers:
         plt.savefig(buffer, format=format)
@@ -78,6 +82,12 @@ def test_savefig_to_stringio_eps():
     _test_savefig_to_stringio(format='eps')
 
 
+@cleanup
+def test_savefig_to_stringio_eps_afm():
+    matplotlib.rcParams['ps.useafm'] = True
+    _test_savefig_to_stringio(format='eps', use_log=True)
+
+
 @cleanup
 @needs_tex
 def test_savefig_to_stringio_with_usetex_eps():
@@ -88,8 +98,8 @@ def test_savefig_to_stringio_with_usetex_eps():
 
 @cleanup
 def test_composite_image():
-    #Test that figures can be saved with and without combining multiple images
-    #(on a single set of axes) into a single composite image.
+    # Test that figures can be saved with and without combining multiple images
+    # (on a single set of axes) into a single composite image.
     X, Y = np.meshgrid(np.arange(-5, 5, 1), np.arange(-5, 5, 1))
     Z = np.sin(Y ** 2)
     fig = plt.figure()
@@ -110,6 +120,7 @@ def test_composite_image():
         buff = ps.read()
         assert buff.count(six.b(' colorimage')) == 2
 
+
 if __name__ == '__main__':
     import nose
     nose.runmodule(argv=['-s', '--with-doctest'], exit=False)