cairo_backend.py: use BytesIO instead of StringIO

This fixes a crash in cairocffi on Python3, and should be compatible
with both python2 and python3. In python2, byte strings are just
strings. In python3, when getting binary data, the user probably wants
a byte string instead of a regular string.

1 files changed, 3 insertions, 6 deletions

diff --git a/gerber/render/cairo_backend.py b/gerber/render/cairo_backend.py
index df4fcf1..d7026b8 100644
--- a/gerber/render/cairo_backend.py
+++ b/gerber/render/cairo_backend.py
@@ -25,10 +25,7 @@ from .render import GerberContext, RenderSettings
 from .theme import THEMES

 from ..primitives import *

 

-try:

-    from cStringIO import StringIO

-except(ImportError):

-    from io import StringIO

+from io import BytesIO

 

 

 class GerberCairoContext(GerberContext):

@@ -125,9 +122,9 @@ class GerberCairoContext(GerberContext):
             self.surface.write_to_png(filename)

 

     def dump_str(self):

-        """ Return a string containing the rendered image.

+        """ Return a byte-string containing the rendered image.

         """

-        fobj = StringIO()

+        fobj = BytesIO()

         self.surface.write_to_png(fobj)

         return fobj.getvalue()