'NameError: name 'vfs' is not defined' SOLVED

EDIT: Never mind. I forgot the import direct.directbase.DirectStart line. Problem solved.

I am new to particles and am trying to experiment with them, so please bear with me as I am a noob.

I have been trying to learn how Panda3D’s particle system works, but the documentation in the manual is sparse. So I tried looking through Akuryou’s code he used in his flight game to generate particles for the contrails. After finding it simpler than I expected, I attempted to recreate this effect for myself.

Then I encountered this error:

This baffled me, as that is Panda source code, and none of it had been altered between the game I used as a model (which ran smoothly, without incident) and my test. I even used the same .ptf file that the game used. Any help would be wonderful.