Avoid name clashes with standard modules

[Layne Lund]

A user can upload a script named json.py or math.py, for example. Other scripts that import json or import math will import these files instead of the standard modules. We need a way to prevent this. Possible solutions are

1. Provide user directories or some other namespacing mechanism
2. Modify file names as they are saved on the server’s file system so don’t clash with standard modules.

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