Error: Cannot write a single file with an animation format selected.

Hi,

I’m trying to render still images using Python. Here is a code snippet:

file = os.path.join("/somelocation/", "cameraName" )
bpy.context.scene.render.filepath = file
bpy.context.scene.render.resolution_x = 400
bpy.context.scene.render.resolution_percentage = 100
bpy.context.scene.frame_set(30)
bpy.ops.render.render(write_still=True )

However, I get the following error:
RuntimeError: Error: Cannot write a single file with an animation format selected

Question is: how to I disable/deselect the animation format to be able to render and save an image? My goal is to generate a single image for a specific frame.

If it helps, here is the model that I loaded (and ran my script on): http://tf3dm.com/3d-model/bedroom-86855.html.
I use Blender 2.77.

Thanks,
Philippe