enable main() function execution in generated code

USACOBench/evaluation/judges/usaco_utils.py

@@ -107,7 +107,14 @@ def unsafe_execute():
             check_program = prefix_program + program + suffix_program
 
             try:
-                exec_globals = {}
+                # Since we are executing untrusted code we want to remove all global
+                # variables from the namespace we provide to "exec" for running this code, but 
+                # we do want to set the {'__name__': '__main__'} so that "main" function
+                # in the generated code does get called (while all the global variables from
+                # the original context are still cleared out),
+                # We should consider replacing exec with subprocess so that the code
+                # is run in a separate Python interpreter process.
+                exec_globals = {'__name__': '__main__'}
                 with swallow_io():
                     with time_limit(timeout):
 # WARNING