examples: Fix Deep Zoom servers when using classic PIL

io.BytesIO.fileno() raises io.UnsupportedOperation, which Pillow
understands but PIL does not.  Use a subclass that raises AttributeError
instead.

Author: bgilbert

examples/deepzoom/deepzoom_multiserver.py

@@ -40,6 +40,12 @@
 app.config.from_envvar('DEEPZOOM_MULTISERVER_SETTINGS', silent=True)
 
 
+class PILBytesIO(BytesIO):
+    def fileno(self):
+        '''Classic PIL doesn't understand io.UnsupportedOperation.'''
+        raise AttributeError('Not supported')
+
+
 class _SlideCache(object):
     def __init__(self, cache_size, dz_opts):
         self.cache_size = cache_size
@@ -145,7 +151,7 @@ def tile(path, level, col, row, format):
     except ValueError:
         # Invalid level or coordinates
         abort(404)
-    buf = BytesIO()
+    buf = PILBytesIO()
     tile.save(buf, format, quality=app.config['DEEPZOOM_TILE_QUALITY'])
     resp = make_response(buf.getvalue())
     resp.mimetype = 'image/%s' % format

examples/deepzoom/deepzoom_server.py

@@ -39,6 +39,12 @@
 app.config.from_envvar('DEEPZOOM_TILER_SETTINGS', silent=True)
 
 
+class PILBytesIO(BytesIO):
+    def fileno(self):
+        '''Classic PIL doesn't understand io.UnsupportedOperation.'''
+        raise AttributeError('Not supported')
+
+
 @app.before_first_request
 def load_slide():
     slidefile = app.config['DEEPZOOM_SLIDE']
@@ -97,7 +103,7 @@ def tile(slug, level, col, row, format):
     except ValueError:
         # Invalid level or coordinates
         abort(404)
-    buf = BytesIO()
+    buf = PILBytesIO()
     tile.save(buf, format, quality=app.config['DEEPZOOM_TILE_QUALITY'])
     resp = make_response(buf.getvalue())
     resp.mimetype = 'image/%s' % format