Raise exception when data is not a valid image

bash_kernel.py

@@ -14,7 +14,8 @@ __version__ = '0.2'
 
 version_pat = re.compile(r'version (\d+(\.\d+)+)')
 
-_TEXT_SAVED = "bash_kernel: saved image data to:"
+_TEXT_SAVED_IMAGE = "bash_kernel: saved image data to:"
+
 
 class BashKernel(Kernel):
     implementation = 'bash_kernel'
@@ -60,7 +61,7 @@ class BashKernel(Kernel):
             cat > $TMPFILE
             echo "%s $TMPFILE" >&2
         }
-        """ % _TEXT_SAVED
+        """ % _TEXT_SAVED_IMAGE
         self.bashwrapper.run_command(bash_rc)
 
     def do_execute(self, code, silent, store_history=True,
@@ -90,8 +91,13 @@ class BashKernel(Kernel):
 
             # Send images, if any
             for filename in image_filenames:
-                self.send_response(self.iopub_socket, 'display_data',
-                                   display_data(filename))
+                try:
+                    data = display_data(filename)
+                except ValueError as e:
+                    message = {'name': 'stdout', 'text': str(e)}
+                    self.send_response(self.iopub_socket, 'stream', message)
+                else:
+                    self.send_response(self.iopub_socket, 'display_data', data)
 
         if interrupted:
             return {'status': 'abort', 'execution_count': self.execution_count}
@@ -139,9 +145,12 @@ class BashKernel(Kernel):
 def display_data(filename):
     with open(filename, 'rb') as f:
         image = f.read()
+    unlink(filename)
 
     image_type = imghdr.what(None, image)
-    if image_type:
+    if image_type is None:
+        raise ValueError("Not a valid image: %s" % image)
+
     image_data = urllib.parse.quote(base64.b64encode(image))
     content = {
         'source': 'kernel',
@@ -149,15 +158,6 @@ def display_data(filename):
             'image/' + image_type: image_data
         }
     }
-    else:
-        content = {
-            'source': 'kernel',
-            'data': {
-                'text': "Not a valid image."
-            }
-        }
-
-    unlink(filename)
     return content
 
 
@@ -166,7 +166,7 @@ def extract_image_filenames(output):
     image_filenames = []
 
     for line in output.split("\n"):
-        if line.startswith(_TEXT_SAVED):
+        if line.startswith(_TEXT_SAVED_IMAGE):
             filename = line.rstrip().split(": ")[-1]
             image_filenames.append(filename)
         else: