I'm not totally sure if this is a deliberate feature or a bug, but if it's a feature then it doesn't seem to be documented anywhere I've seen.
In Vault Password, the python builtin function reduce() causes a NameError: name 'reduce' is not defined. The function name still gets syntax-colored gray like other, working, builtin functions such as range(). I'm moderately sure I remember using reduce() in at least one other mission.
NameError: name 'reduce' is not defined
If this behavior is intended, it should be documented somewhere findable, such as the mission description sidebar; otherwise, it should be corrected.
Empire of code uses Python3 which removed reduce() as a builtin function.
Aha, thank you.