Local variables and global variables
in the code below, old_price, rite global variables, final_price for local variables
Globals () declare a global variable, the function may be modified within the outer variable function
Built-in functions: function among nested functions
Closure:
closure condition
1 defines a function within an outer function.
2 function in the use of temporary variables outside the function.
3 and the external function returns a reference to the function value.
