On Google App Engine, I had to display the user-submitted image, if there was one, else display a default image.
The given object could only have one image, so I was using the NDB BlobProperty:
class Sensor(ndb.Model):
image = ndb.BlobProperty()
I put the default image in my application root (alongside app.yaml):
app_root:
request_handlers:
- __init__.py
- handlers.py
- app.yaml
- default_sensor.jpg
...
In my request handler, I checked for the presence of an image, and gave the default image if there wasn’t one there:
# responds to "/sensors/(\w+)/image"
class SensorImage(webapp2.RequestHandler):
DEFAULT_IMAGE = 'default_sensor.jpg'
def get(self, hex):
r = self.response
r.headers['Content-Type'] = "image/jpg"
this_sensor = Sensor.find_by_hex(hex)
if (not this_sensor) or (not this_sensor.image):
image = open(SensorImage.DEFAULT_IMAGE, 'rb')
r.body_file.write( image.read() )
image.close()
else:
r.body_file.write( this_sensor.image )
That way, I had one URL that didn’t change whether a user uploaded an image or not.