use __import__ instead of exec

graders/lab1.py

@@ -16,7 +16,7 @@ sys.path.insert(0, path.expanduser('~/submissions'))
 sys.dont_write_bytecode = True
 
 def run():
-	exec("import %s as submission" % importname)
+	submission = __import__(importname)
 	if submission.test() == 1:
 		return 100
 	else:

graders/lab2.py

@@ -17,7 +17,7 @@ sys.dont_write_bytecode = True
 
 output = ''
 def run():
-	exec("import %s as submission" % importname)
+	submission = __import__(importname)
 	global output
 	score = 0
 

graders/lab3.py

@@ -36,7 +36,7 @@ pizfiles = [('handout.piz', 3950), ('invalid.piz', 1050)]
 output = ''
 score = 0
 def run():
-	exec("import %s as submission" % importname)
+	submission = __import__(importname)
 	global output, score
 
 	pizzas = [