Yes, it is. What is the value of str(5/i)? If i can't be redefined you can always replace i with its definition. If i can be redefined what string str(5/i) will

Yes, it is. What is the value of str(5/i)? If i can't be redefined you can always replace i with its definition. If i can be redefined what string str(5/i) will evaluate to may be impossible to deduce a priori. Both the programmer and the compiler can replace i with its definition when it sees the expression "str(5/i)". That freedom is lost when the language allows rebinding.